sched/fair: Skip pulling tasks from cpu marked for active balancing

Idle/newly idle cpu finds busiest runqueue to pull tasks from it.
It is possible that, the busiest cpu might have already marked for
active_balance by other cpu. But current balancing cpu still finds
it as busiest cpu and tries to pull tasks from it.

Which may have subtle impact, if higher capacity cpu has marked busy
cpu for active balance, and before active balance kicks in by the
busy cpu, the lower capacity cpu pulling tasks from the busy cpu
ruins the higher capacity cpu's active balance.

Fix this, by skipping the cpu which is undergoing active_balance
for finding busiest queue and do not detach tasks if busiest cpu
marked for active balance.

Change-Id: If3ebe1a026cf62f055bb42c3f3ed62f3624c704a
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>