Fix skip checks in volume and snapshot manage tests

In volume and snapshot manage tests, misconfiguration of parameter
'manage_volume_ref' or 'manage_snapshot_ref' should lead the test
to fail, not skip the test. This patch is to raise InvalidConfiguration
exception when these two config parameters misconfigured.

Change-Id: I4038047e9ec734acdf01b5ece9962964f236ffdd
2 files changed