Don't fall when just loading octaviav2 modules

this avoids loading warnings on salt-master that may not have
os-client-config installed, as salt tries to load them irrespective of
__virtual__() result.

Change-Id: I37bc581b10aa2876597dd2bc6b51015ee31cc4f2
Related-Issue: https://mirantis.jira.com/browse/PROD-27276
(cherry picked from commit ce6159b430d455b3febdf039138c1ce074de9b39)
diff --git a/_modules/octaviav2/common.py b/_modules/octaviav2/common.py
index 7cccf0b..ddc8138 100644
--- a/_modules/octaviav2/common.py
+++ b/_modules/octaviav2/common.py
@@ -1,7 +1,13 @@
 import logging
-import os_client_config
 from uuid import UUID
 
+try:
+    import os_client_config
+except ImportError:
+    os_client_config = None
+from salt import exceptions
+
+
 log = logging.getLogger(__name__)
 
 
@@ -39,6 +45,10 @@
 
 
 def _get_raw_client(cloud_name):
+    if not os_client_config:
+        raise exceptions.SaltInvocationError(
+            "Cannot load os-client-config. Please check your environment "
+            "configuration.")
     service_type = 'load-balancer'
     config = os_client_config.OpenStackConfig()
     cloud = config.get_one_cloud(cloud_name)