LU-15097 quota: stop pool_recalc before killing pool

LU-15097 quota: stop pool_recalc before killing pool

qmt_start_pool_recalc holds a refrence on a pool while
it is running. This thread should be stopped before
putting the last pool reference in qmt_pool_free to be
sure that pool can finally freed. Patch helps to avoid
following ASSERTION:
qmt_pool_fini()) ASSERTION( list_empty(&qmt->qmt_pool_list) ) failed

HPE-bug-id: LUS-10294
Change-Id: If72042a620d9ded693fcb669bc9148d1f96126a4
Signed-off-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-on: https://review.whamcloud.com/45256
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Andriy Skulysh <andriy.skulysh@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>