LU-13131 osc: Do not wait for grants for too long

LU-13131 osc: Do not wait for grants for too long

obd_timeout is way too long considering we are holding a lock
that might be contended. If OST is slow to respond, we might
get evicted, so limit us to a half of the shortest possible
max wait a server might have before switching to synchronous IO.

Lustre-change: https://review.whamcloud.com/38283
Lustre-commit: 1eee11c75ca13745d083410e1ced3a1a8b088ee9

Change-Id: I36653194c1b8b95ba3cc2ed9240df7b0888cf7ed
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/38672
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>