aiopcpu is an exceptionally cryptic name that doesn't mean anything to
most people reading test results. multinode is what the job is, and is
much more understandable at first glance.
This changes the naming from aiopcpu => multinode. Should we create a
different kind of multinode test in the future, we can come up with an
appropriate name for it then.
This is safe to change because the devstack-gate logic actually is
fully != 'aio', not == 'aiopcpu'.
Change-Id: Ic7fe31a397af8a14ecf33a4902908ff9c03d11d3
f06ca68f94