Store all of the master's persistent data on a separate "data"
persistent disk when running on GCE.

I'll follow up soon with a second PR that enables kube-push to
completely bring down the master VM and replace it with a new one.
Fix the e2e test to remove a race.
Merge pull request #3034 from a-robinson/pd-up

Store all of the master's persistent data on a separate "data" PD when running on GCE
Merge pull request #3040 from brendandburns/pd2

Fix the update e2e test to remove a race.