Update error messages in sanity tests

Update error messages throughout sanity tests
to use the same (or similar) format of error message.

Change-Id: I4db0517a5b264151ddaa6ea2c2a04d37e139944e
Related-PROD: #PROD-32415
diff --git a/test_set/cvp-sanity/tests/test_cinder_services.py b/test_set/cvp-sanity/tests/test_cinder_services.py
index a612bca..9e13e36 100644
--- a/test_set/cvp-sanity/tests/test_cinder_services.py
+++ b/test_set/cvp-sanity/tests/test_cinder_services.py
@@ -13,8 +13,9 @@
     service_down = local_salt_client.cmd_any(
         tgt='keystone:server',
         param='. /root/keystonercv3; cinder service-list | grep "down\|disabled"')
-    assert service_down == '', \
-        '''Some cinder services are in wrong state'''
+    assert service_down == '', (
+        "Some Cinder services are in wrong state:\n{}".format(service_down))
+
 
 @pytest.mark.full
 def test_cinder_services_has_all_backends(local_salt_client, check_cinder_backends):
@@ -30,7 +31,7 @@
         tgt='keystone:server',
         param='. /root/keystonercv3; cinder service-list | grep "volume" |grep -c -v -e "lvm"')
     backends_num = len(backends_cinder.keys())
-    assert cinder_volume == str(backends_num), \
-        'Number of cinder-volume services ({0}) does not match ' \
-        'number of volume backends ({1})'.format(
-        cinder_volume, str(backends_num))
+    assert cinder_volume == str(backends_num), (
+        'Number of cinder-volume services ({0}) does not match number of '
+        'volume backends ({1}).'.format(cinder_volume, str(backends_num))
+    )