Automatic merge from submit-queue
Add e2e tests for storageclass
- test pd-ssd and pd-standard on GCE,
- test all four volume types and encryption on AWS
- test just the default volume type on OpenStack (right now, there is no API
to get list of them)
These tests are quite slow, e.g. there are two tests on AWS that has to run mkfs.ext4 on 500 GB magnetic drive with low IOPS, which takes ~3-4 minutes each.