Add more information to BuildErrorException

This commit adds expected_status to BuildErrorException. This is helpful
for checking the error details.

Change-Id: I2979d39467daeb06793081b83e3a5b81b7d5623e
Closes-bug: #1265559
Skip EC2VolumesTest if Cinder is not available

While other volume tests are skipped if Cinder is not available,
such skips are not present in the EC2 tests.

Change-Id: I9f28cf5ea094c0ae2cd6522e15318aada354a369
Closes-Bug: 1282833
Merge "Add more information to BuildErrorException"
Merge "Skip EC2VolumesTest if Cinder is not available"