Increase CPU flavor for CI (#4389)

tests/files/gce_centos7-multus-calico.yml

 # Instance settings
 cloud_image_family: centos-7
 cloud_region: us-central1-c
-cloud_machine_type: "n1-standard-1"
+cloud_machine_type: "n1-standard-2"
 mode: default
 
 # Deployment settings

tests/files/gce_coreos-kube-router.yml

 # Instance settings
 cloud_image_family: coreos-stable
 cloud_region: us-central1-c
+cloud_machine_type: "n1-standard-2"
 mode: default
 startup_script: 'systemctl disable locksmithd && systemctl stop locksmithd'
 

tests/files/gce_ubuntu-flannel-ha.yml

 # Instance settings
 cloud_image_family: ubuntu-1604-lts
 cloud_region: us-central1-b
-cloud_machine_type: "n1-standard-1"
+cloud_machine_type: "n1-standard-2"
 mode: ha
 
 # Deployment settings

tests/files/gce_ubuntu-kube-router-sep.yml

 # Instance settings
 cloud_image_family: ubuntu-1604-lts
 cloud_region: us-central1-c
+cloud_machine_type: "n1-standard-2"
 mode: separate
 
 # Deployment settings