Add call_retry for ModelBuilder for error recovery

Add call_retry method for ModelBuilder classes along with configuration
options. This allows ModelBuilder classes to reattempt any failed calls
to external services such as Nova or Ironic.

Change-Id: Ided697adebed957e5ff13b4c6b5b06c816f81c4a

watcher/conf/collector.py

@@ -35,6 +35,13 @@ Supported in-tree collectors include:
 Custom data model collector plugins can be defined with the
 ``watcher_cluster_data_model_collectors`` extension point.
 """),
+    cfg.IntOpt('api_call_retries',
+               default=10,
+               help="Number of retries before giving up on external service "
+                    "calls."),
+    cfg.IntOpt('api_query_timeout',
+               default=1,
+               help="Time before retry after failed call to external service.")
 ]