sched/core: Keep rq online after cpu isolation

To move tasks off a cpu when offlining the rq needs to be offlined to
un-throttle tasks.  However, tasks might still run on the CPU even after
the CPU has been isolated (per-CPU threads). Thus we should leave the rq
in online state after tasks have been moved.

Change-Id: I61486e8648af0dbb82595fe699e1bc158e837362
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>