LU-11196 tests: clean up after conf-sanity test_101

LU-11196 tests: clean up after conf-sanity test_101

conf-sanity test_101() creates up to 50000 files in the top-level
test directory, which can sometimes cause the later test_103() setup
to fail, because "rm -rf" fails with "Argument list too long" when
trying to clean up the test directory.

Create the test_101 files in a subdirectory for cleanliness, and
remove them at the end of the test so that we don't run out of space.

This patch is back-ported from the following one:
Lustre-commit: ed44caee9af0eeb32bce7e7de5f5146fa6dc1d00
Lustre-change: https://review.whamcloud.com/33268

Test-Parameters: trivial testlist=conf-sanity
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I1167339d03340e1cc545d2855c4b32eef18cab07
(cherry picked from commit ed44caee9af0eeb32bce7e7de5f5146fa6dc1d00)
Reviewed-on: https://review.whamcloud.com/33495
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>