EndpointNotFound deleting volume backend instance

When there is some error in volume creating on booting from volume,
we may get the EndpointNotFound exception when deleting the error instance.
Then we can never delete the instance successfully. The exception should
be ignored.

Change-Id: Ia92b648eb18c70996747d361e227de771f33ee9c
Closes-bug: 1346866
Merge "EndpointNotFound deleting volume backend instance"