LU-11917 tests: wait for test_257 to finish recovery

The sanity test_257 restarts the MDS, but it may still be in
recovery at the start of test_260a and cause failures.  Wait for
recovery to complete before the end of test_257.

Fixes: 1cb9e85039c ("LU-7433 ldlm: xattr locks are lost on mdt")
Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I00f183938a208608155ca71b08ca7977903ebbe5
Reviewed-on: https://review.whamcloud.com/34165
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>