LVM volume_clear: error on unexpected inputs

Currently if a user configures
volume_clear='non_existent_volume_clearer' in cinder.conf,
the LVM driver will silently delete a volume and not wipe it.

Instead, the delete operation should fail, leaving the volume
in the 'error_deleting' state.

Also fail if the volume reference does not contain either a
'size' or 'volume_size' field.

Closes-Bug: #1225194
Change-Id: I78fec32d7d5aeaa8e2deeac43066ca5e2e26d9ca
Merge "LVM volume_clear: error on unexpected inputs"