[algorithm][Algorithm] Add loop_user type

This is a specific type for algorithm using loop as they have
additional constraints with regards to classic autonomous
algorithms.

beat/backend/python/algorithm.py

@@ -381,6 +381,7 @@ class Algorithm(object):
     SEQUENTIAL = 'sequential'
     AUTONOMOUS = 'autonomous'
     LOOP = 'loop'
+    LOOP_USER = 'loop_user'
 
 
     def __init__(self, prefix, name, dataformat_cache=None, library_cache=None):