3PAR volume detach with host in a host set

When deleting the last VLUN for a host, try to
delete the host.  If the host is in a host set
this will fail.  When that happens, log a nice
message including the reason, but don't fail
or hang the delete VLUN.  Leave hosts in host
sets.

Closes-Bug: #1317134

Change-Id: Ie3f8f94c05a6a318de866598f9e9c4c5d84926f4
Merge "3PAR volume detach with host in a host set"