LU-15571 tests: save/restore debug mask for interop

LU-15571 tests: save/restore debug mask for interop

The "createmany" and "unlinkmany" wrappers were saving the debug
mask on the client and restoring it on the server, which fails in
interop testing if the client has a debug mask set that is unknown
on the server.

Use the debugsave() and debugrestore() helpers to do this properly.

Fixes: 40d286e11138 ("LU-15317 llite: Add D_IOTRACE")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I36fc06d5a62e34d63619fa977d9f80254bbc073e
Reviewed-on: https://review.whamcloud.com/46636
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>