Increase timeout for manifest delete/refresh (#359)

Default value for timeout is 5 minutes. Subscription upload takes more
time and as an exclusion has timeout of 15 minutes.
Automation results uncovered manifest delete/refresh commands take
pretty much comparable with upload amount of time (latest run shows
they took ~7 mins), which causes failures.
Updating timeout for manifest delete/refresh to match upload, hopefully
this will help us to get rid of constant subscription test failures.

nailgun/entities.py

@@ -4965,7 +4965,12 @@ def delete_manifest(self, synchronous=True, **kwargs):
             self._org_path('delete_manifest', kwargs['data']),
             **kwargs
         )
-        return _handle_response(response, self._server_config, synchronous)
+        return _handle_response(
+            response,
+            self._server_config,
+            synchronous,
+            timeout=900,
+        )
 
     def manifest_history(self, synchronous=True, **kwargs):
         """Obtain manifest history for subscriptions.
@@ -5005,7 +5010,12 @@ def refresh_manifest(self, synchronous=True, **kwargs):
             self._org_path('refresh_manifest', kwargs['data']),
             **kwargs
         )
-        return _handle_response(response, self._server_config, synchronous)
+        return _handle_response(
+            response,
+            self._server_config,
+            synchronous,
+            timeout=900,
+        )
 
     def upload(self, synchronous=True, **kwargs):
         """Upload a subscription manifest.