Add parameter to specify configuration section to load for databases_provider

With the current implementation, the configuration of the execution process may contain two entries:

1. Main algorithm
2. Loop algorithm

The way the databases provider works will only load the main entry which means that it will use the wrong configuration for the loop algorithm. This new parameter allows to set which entry should be used to configure the database. The default is None so the default behaviour doesn't change.

beat/backend/python/scripts/databases_provider.py

@@ -29,15 +29,16 @@
 """Executes some database views. (%(version)s)
 
 usage:
-  %(prog)s [--debug] <addr> <dir> <cache>
+  %(prog)s [--debug] <addr> <dir> <cache> [<conf_name>]
   %(prog)s (--help)
   %(prog)s (--version)
 
 
 arguments:
-  <addr>  Listen for incoming request on this address ('host:port')
-  <dir>   Directory containing all configuration required to run the views
-  <cache> Path to the cache
+  <addr>        Listen for incoming request on this address ('host:port')
+  <dir>         Directory containing all configuration required to run the views
+  <cache>       Path to the cache
+  <conf_name>   Name of the configuration to load
 
 
 options:
@@ -55,6 +56,7 @@ import docopt
 import simplejson
 import pwd
 import stat
+import json
 
 import zmq
 
@@ -167,10 +169,26 @@ def main(arguments=None):
         database_cache = {}
 
         try:
+            configuration_path = os.path.join(args['<dir>'], 'configuration.json')
+            if not os.path.exists(configuration_path):
+                raise RuntimeError("Configuration file '%s' not found" %
+                                   configuration_path)
+
+            with open(configuration_path) as f:
+                configuration_data = json.load(f)
+
+            configuration_name = args.get('<conf_name>', None)
+            if configuration_name is not None:
+                configuration_data = configuration_data.get(configuration_name,
+                                                            None)
+                if configuration_data is None:
+                    raise RuntimeError("Configuration section '%s' not found" %
+                                       configuration_name)
+
             dbexecutor = DBExecutor(message_handler,
                                     os.path.join(args['<dir>'], 'prefix'),
                                     args['<cache>'],
-                                    os.path.join(args['<dir>'], 'configuration.json'),
+                                    configuration_data,
                                     dataformat_cache,
                                     database_cache)
         except (MemoryError):