LU-12905 tests: wrappers for createmany and unlinkmany

LU-12905 tests: wrappers for createmany and unlinkmany

which set debug=0 if number of operations is high enough.
this is to speedup testing.

according to Maloo sanity in review-ldiskfs takes ~9min less.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I0e0a0ef6cf217ecddd1b780103d01e2109fc33d9
Reviewed-on: https://review.whamcloud.com/36585
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>