Support cross-tenant metrics in monasca collector

This allows metrics to be fetched from the current scope in the monasca
collector, in case cross-metric tenant submission is enabled: https://github.com/openstack/monasca-agent/blob/master/docs/MonascaMetrics.md#cross-tenant-metric-submission.

Story: 2006696
Task: 36999
Change-Id: Icd32a2d0be249efea0867d8a2966c156084e75bb

cloudkitty/collector/monasca.py

@@ -179,7 +179,11 @@ class MonascaCollector(collector.BaseCollector):
         extra_args = self.conf[metric_name]['extra_args']
         kwargs = {}
         if extra_args['forced_project_id']:
-            kwargs['tenant_id'] = extra_args['forced_project_id']
+            if extra_args['forced_project_id'] == 'SCOPE_ID' and project_id:
+                kwargs['tenant_id'] = project_id
+                dimensions.pop(CONF.collect.scope_key, None)
+            else:
+                kwargs['tenant_id'] = extra_args['forced_project_id']
 
         return self._conn.metrics.list_statistics(
             name=metric_name,

doc/source/admin/configuration/collector.rst

@@ -274,7 +274,9 @@ Monasca
   fetched from a specific tenant instead of the one cloudkitty is identified
   in. For example, if cloudkitty is identified in the ``service`` project, but
   needs to fetch a metric from the ``admin`` project, its ID should be
-  specified through this option.
+  specified through this option. If this option is set to ``SCOPE_ID``,
+  the metric will be fetched from the current project (this assumes that
+  scopes are configured to be projects/tenants).
 
 Prometheus
 ~~~~~~~~~~

releasenotes/notes/support-cross-tenant-metric-submission-monasca-collector-508b495bc88910ca.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Cross-tenant metric submission is now supported in the monasca collector.
+    In order to a fetch metric from the scope that is currently being processed,
+    the ``forced_project_id`` option must be set to ``SCOPE_ID``.