updating default OS as previous one is removed

Google no longer has coreos_1235.9.0 available as an image. This causes failed deployments if users plan to install this. The change allows the default to be coreos_1235.12.0. Users can always control their values with their own `desired_cluster_profile.tfvars`.

Author: bernadinm

gcp/modules/dcos-tested-gcp-oses/gcp_variables.tf

@@ -19,6 +19,7 @@ variable "gcp_os_image_version" {
   "centos_7.2"                = ["centos-cloud","centos-7-v20170523"]
   "centos_7.3"                = ["centos-cloud","centos-7-v20170719"]
   "coreos_1235.9.0"           = ["coreos-cloud", "coreos-stable-1235-9-0-v20170202"]
+  "coreos_1235.12.0"          = ["coreos-cloud", "coreos-stable-1235-12-0-v20170223"]
   "rhel_7.3"                  = ["rhel-cloud", "rhel-7-v20170523"]
  }
 }

gcp/modules/dcos-tested-gcp-oses/platform/cloud/gcp/coreos_1235.12.0/setup.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+sudo systemctl disable locksmithd
+sudo systemctl stop locksmithd
+sudo systemctl restart docker # Restarting docker to ensure its ready. Seems like its not during first usage.

gcp/variables.tf

@@ -62,8 +62,8 @@ variable "gcp_scheduling_preemptible" {
 }
 
 variable "os" {
-  default = "coreos_1235.9.0"
-  description = "Recommended DC/OS OSs are centos_7.2, coreos_1235.9.0, coreos_835.13.0"
+  default = "coreos_1235.12.0"
+  description = "Recommended DC/OS OSs are centos_7.2, coreos_1235.12.0, coreos_835.13.0"
 }
 
 variable "num_of_private_agents" {