collect isolated capacity using a cache plugin, not stdout parsing

reading capacity values using the jsonfile cache plugin is more robust
in scenarios where ansible-playbook may print non-JSON output (such as
-vvv or when a custom callback plugin like timer is enabled)

awx/plugins/isolated/awx_capacity.py

@@ -62,7 +62,12 @@ def main():
 
     # Module never results in a change
     module.exit_json(changed=False, capacity_cpu=capacity_cpu,
-                     capacity_mem=capacity_mem, version=version)
+                     capacity_mem=capacity_mem, version=version,
+                     ansible_facts=dict(
+                         awx_capacity_cpu=capacity_cpu,
+                         awx_capacity_mem=capacity_mem,
+                         awx_capacity_version=version
+                     ))
 
 
 if __name__ == '__main__':