tests: harden systest further against instance creation timeout (#209)

Closes #208

Author: tseaver

packages/google-cloud-bigtable/tests/system.py

@@ -288,7 +288,7 @@ def test_create_instance_w_two_clusters(self):
         self.instances_to_delete.append(instance)
 
         # We want to make sure the operation completes.
-        operation.result(timeout=60)
+        operation.result(timeout=120)
 
         # Create a new instance instance and make sure it is the same.
         instance_alt = Config.CLIENT.instance(ALT_INSTANCE_ID)