Automatic merge from submit-queue

Ensure object returned by volume getCloudProvider incorporates cloud config

This PR addresses https://github.com/kubernetes/kubernetes/issues/23517.

**Problem**
The existing GCE PD and AWS EBS volume plugin code were fetching cloud provider without specifying a cloud config: `cloudprovider.GetCloudProvider("gce", nil)`
This caused the cloud provider to use default auth mechanism, which is not acceptable for the provisioning controller running on GKE master.

**Fix**
This PR does the following:
* Modifies the GCE PD and AWS EBS volume plugin code to use the cloud provider object pre-constructed by the binary with a cloud config.
* Enable provisioning E2E test for GKE (to catch future issues).

Thanks to @cjcullen for debugging and finding the root cause!  👍 

This should be cherry-picked into the v1.2 branch for the next release.