Fix ubuntu-contiv test failed (#3808)

netchecker agent status is pending

tests/files/gce_ubuntu-contiv-sep.yml

@@ -1,6 +1,7 @@
 # Instance settings
 cloud_image_family: ubuntu-1604-lts
 cloud_region: us-central1-b
+cloud_machine_type: "n1-standard-2"
 mode: separate
 
 # Deployment settings