CA-115429: Fixed: Deletion of snapshot is successful but XenCenter logs ...

...show error.

XAPI (from 1.7) destroy destroys suspend VDIs as well (code is here: xapi: ocaml/xapi/cli_operations.ml). Depending on actual race conditions, this can lead to a situation when we try to destroy a Suspend VDI that has just been deleted.

Signed-off-by: Gabor Apati-Nagy <gabor.apati-nagy@citrix.com>