LU-15150 tests: sanity-lnet removes testsuite log on failure

LU-15150 tests: sanity-lnet removes testsuite log on failure

cleanup_testsuite() needs to be more selective when removing files
created by sub-tests.

Test-Parameters: trivial testlist=sanity-lnet
Fixes: aa739144551 ("LU-13569 tests: Check LNet Health recovery logic")
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: Ic17a68ff2aa552594a0f1ea470c39177abe985fc
Reviewed-on: https://review.whamcloud.com/45342
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>