Catch ImageNotFound exception when deleting rbd volume

When deleting a rbd volume it is possible for remove() to
throw a ImageNotFound exception. In this case we should
catch the exception, so the volume delete can continue.

Closes-Bug: 1403172
Change-Id: I32cf9d3774c129cda4449996ceeb4b43b7e42904
(cherry picked from commit ddc8d7a4233aee139f9c91aeee885d7f2e45f8ac)
Merge "Catch ImageNotFound exception when deleting rbd volume" into stable/juno