Fix inability to delete volumes in error state for NetApp driver

Fix inability to delete volumes in error state for NetApp driver

While using NetApp 7-mode storage box to create volumes, if the volume
is not created on the storage box (possibly due to wrong/missing
options in cinder.conf file), the volume goes in error state, and when
one tries to delete the volume, an exception was raised which made
the volume go in error_deleting state, which is unrecoverable. This
commit quiesces that exception, resulting in successful removal of the
volume entry from the volume table.

Fixes bug 1090167

Change-Id: I0a25b71ad03e7f7acf58df3952e074ff164b82ff