revert 666f0b56 (CA-122253)

This commit reverts "CA-122253: Improve error reporting for LVM-based SR
snapshots" as it hasn't been tested by a storage BST and the imminent
backout merge from trunk-storage into trunk could introduce regressions.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

GitHub: closes #65 on xapi-project/github