The ability to enable multiattach on the command line was deprecated in
Queens with the full implementation of multiattach enabling it through
volume type extra specs. This removes the command line arg and handling
for specifying it with volume creation.
Change-Id: Ifc0c874657f959266050cd1a7a40e6ecccc8c114
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>