Add more retries to allow manila backup restore to complete

Due to slow 1GiB networking in ServerStack the restore often exceeds the
retries.  Increase them to enable the restore to succeed.

zaza/openstack/charm_tests/manila/tests.py

@@ -359,7 +359,7 @@ packages:
             self.manila_client.shares,
             share.id,
             wait_iteration_max_time=120,
-            stop_after_attempt=2,
+            stop_after_attempt=10,
             expected_status="available",
             msg="Waiting for a share to become available")