EX-7795 tests: add sanity-compr test for dir compression

EX-7795 tests: add sanity-compr test for dir compression

This patch adds a sanity-compr test to validate that
we get directory space usage reduction with compression.

Change-Id: I16f3a3f1e413e4884b3973829df36500667271ce
Test-Parameters: trivial testlist=sanity-compr env=ONLY="1007 1008",ONLY_REPEAT=3
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53855
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Colin Faber <cfaber@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>