[prefix] Add algorithm for loop testing

- loop is the validation algorithm
- loop_user is the algorithm communicating with the loop

beat/backend/python/test/prefix/algorithms/autonomous/loop/1.json

+{
+    "schema_version": 2,
+    "language": "python",
+    "api_version": 2,
+    "type": "loop",
+    "splittable": false,
+    "groups": [
+        {
+            "inputs": {
+                "in": {
+                    "type": "user/single_integer/1"
+                }
+            },
+            "outputs": {
+                "out": {
+                    "type": "user/single_integer/1"
+                }
+            }
+        }
+    ]
+}

beat/backend/python/test/prefix/algorithms/autonomous/loop/1.py

+#!/usr/bin/env python
+# vim: set fileencoding=utf-8 :
+
+###############################################################################
+#                                                                             #
+# Copyright (c) 2018 Idiap Research Institute, http://www.idiap.ch/           #
+# Contact: beat.support@idiap.ch                                              #
+#                                                                             #
+# This file is part of the beat.backend.python module of the BEAT platform.   #
+#                                                                             #
+# Commercial License Usage                                                    #
+# Licensees holding valid commercial BEAT licenses may use this file in       #
+# accordance with the terms contained in a written agreement between you      #
+# and Idiap. For further information contact tto@idiap.ch                     #
+#                                                                             #
+# Alternatively, this file may be used under the terms of the GNU Affero      #
+# Public License version 3 as published by the Free Software and appearing    #
+# in the file LICENSE.AGPL included in the packaging of this file.            #
+# The BEAT platform is distributed in the hope that it will be useful, but    #
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY  #
+# or FITNESS FOR A PARTICULAR PURPOSE.                                        #
+#                                                                             #
+# You should have received a copy of the GNU Affero Public License along      #
+# with the BEAT platform. If not, see http://www.gnu.org/licenses/.           #
+#                                                                             #
+###############################################################################
+
+class Algorithm:
+
+    def validate(self, result):
+        value = int(result)
+
+        return value < 6

beat/backend/python/test/prefix/algorithms/autonomous/loop_user/1.json

+{
+    "schema_version": 2,
+    "language": "python",
+    "api_version": 2,
+    "type": "autonomous",
+    "splittable": false,
+    "groups": [
+        {
+            "inputs": {
+                "in": {
+                    "type": "user/single_integer/1"
+                }
+            },
+            "outputs": {
+                "out": {
+                    "type": "user/single_integer/1"
+                }
+            }
+        }
+    ]
+}

beat/backend/python/test/prefix/algorithms/autonomous/loop_user/1.py

+#!/usr/bin/env python
+# vim: set fileencoding=utf-8 :
+
+###############################################################################
+#                                                                             #
+# Copyright (c) 2018 Idiap Research Institute, http://www.idiap.ch/           #
+# Contact: beat.support@idiap.ch                                              #
+#                                                                             #
+# This file is part of the beat.backend.python module of the BEAT platform.   #
+#                                                                             #
+# Commercial License Usage                                                    #
+# Licensees holding valid commercial BEAT licenses may use this file in       #
+# accordance with the terms contained in a written agreement between you      #
+# and Idiap. For further information contact tto@idiap.ch                     #
+#                                                                             #
+# Alternatively, this file may be used under the terms of the GNU Affero      #
+# Public License version 3 as published by the Free Software and appearing    #
+# in the file LICENSE.AGPL included in the packaging of this file.            #
+# The BEAT platform is distributed in the hope that it will be useful, but    #
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY  #
+# or FITNESS FOR A PARTICULAR PURPOSE.                                        #
+#                                                                             #
+# You should have received a copy of the GNU Affero Public License along      #
+# with the BEAT platform. If not, see http://www.gnu.org/licenses/.           #
+#                                                                             #
+###############################################################################
+
+class Algorithm:
+
+    def process(self, data_loaders, outputs, loop_channel):
+        cnt = 100
+        while not loop_channel.is_result_valid(cnt):
+            cnt = cnt - 1
+
+        data_loader = data_loaders.loaderOf('in')
+
+        for i in range(data_loader.count()):
+            (data, start, end) = data_loader[i]
+
+            outputs['out'].write({
+                    'value': data['in'].value,
+                },
+                end
+            )
+        return True