lvmlockd: prevent vgremove of dlm VG while lockspace is used

This applies the same rule/logic to dlm VGs that has always
existed for sanlock VGs.  Allowing a dlm VG to be removed
while its lockspace was still running on other hosts largely
worked, but there were difficult problems if another VG with
the same name was recreated.  Forcing the VG lockspace to
be stopped, gives both sanlock and dlm VGs the same behavior.
4 files changed