Storwize/SVC driver crashes when check volume copy status

Storwize/SVC driver does not clear up property of _vdiskcopyops
when deleting a volume. So if a volume which under async copy is
deleted before sync completed, the driver will crash.

When delete a volume, add a check for _vdiskcopyops, if volume
is in the dict, remove it.

Change-Id: I4905404b72a7ac8f90bd92fa4345ba771a78418b
Closes-Bug: #1304115
Merge "Storwize/SVC driver crashes when check volume copy status"