LU-14102 tests: add a pause in open-close in sanity/160l

LU-14102 tests: add a pause in open-close in sanity/160l

so that close has to update mtime and generate CL_MTIME
record in the changelog.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I118172229c86ed5c201299de7476678689bf4cab
Reviewed-on: https://review.whamcloud.com/40508
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>