LU-14480 pool: wrong usage with ost list

LU-14480 pool: wrong usage with ost list

When the OST list is given on setstripe, it should have a priority
over the pool. Also, we check only for the 1st OST if it is in the
pool at the creation time, what worked well in past with -c and
works even with -C, but not with the OST list when some of the OSTs
are out of the pool.

Make the --pool and --ost options mutualy exclusive.
Drop the pool inheritance if the OST list is given.

Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: I94a7fe97391f1185392f986f78ab1a372238972a
Reviewed-on: https://es-gerrit.dev.cray.com/158198
HPE-bug-id: LUS-9579
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Tested-by: Elena Gryaznova <c17455@cray.com>
Reviewed-on: https://review.whamcloud.com/41815
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Andriy Skulysh <askulysh@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>