LU-13184 tests: wait for OST startup in test_112

Wait for OST0000 to finish mounting and connecting to the MDS before
forcing to create any files there.  Otherwise, intermittent failures
are seen because the OST has no objects and returns -ERANGE:

    lfs setstripe: 'f112.conf-sanity.0': Numerical result out of range
    problem creating f112.conf-sanity.0 on OST0000

Test-Parameters: trivial testlist=conf-sanity envdefinitions=ONLY=112,ONLY_REPEAT=100
Fixes: 416e67222b76 ("LU-12036 ofd: add 'no_precreate' mount option")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: If2d547a42c51a7028803ec25680931a7593ebbe5
Reviewed-on: https://review.whamcloud.com/37393
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>