LU-2225 tests: sanity/27 tests to poll for state

LU-2225 tests: sanity/27 tests to poll for state

- reset_enospc() to poll when precreate_status is OK
- exhaust_precreations() to wait one time, not for every OST

ONLY=27 OSTCOUNT=7 sh sanity: 641 sec before and 373 sec after

Test-Parameters: trivial testlist=sanity fstype=zfs
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I97366cb046c50223020f2161603657056a602cd5
Reviewed-on: https://review.whamcloud.com/4388
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>