EX-3875 lustre: add allow_intr param to mdc and osc

EX-3875 lustre: add allow_intr param to mdc and osc

Add an obd_import parameter ("allow_intr") to make all requests from a
given import interruptible. Remove hot-pools test_16() from
ALWAYS_EXCEPT.

Remove the unconditional setting of allow_intr added by EX-3749 mdc:
non blocking close and changelog release.

Lustre-change: https://review.whamcloud.com/45005
Lustre-commit: c5803ee670b57d05568f4c0ef527be6977772540

Test-Parameters: trivial testlist=hot-pools env=ONLY=16,ONLY_REPEAT=20
Change-Id: Ibc258a0e89dab204f2a10ba29e3eea19030ad444
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/45129
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>