Deactivate LV before removing

With certain versions of LVM2, removing an active LV can end up with

  Unable to deactivate open XXX
  libdevmapper exiting with 1 device(s) still suspended.

which causes any lvm command afterwards to hang endlessly on
trying to access the suspended volume. This seems to be caused
by a race with udev, so lets be conservative and do the deactivation,
then wait for udev and then finish the removal.

Closes-Bug: #1270192

Change-Id: I4703133180567090878ea5047dd29d9f97ad85ab
Merge "Deactivate LV before removing"