EX-8362 scripts: improve ll_compression_scan estimate

EX-8362 scripts: improve ll_compression_scan estimate

Improve ll_compression_scan script to give a better estimate of
actual compression ratios.
- add a '-d' debug option for verbose output during testing
- log and report incompressible small files < 4096
- log and report incompressible file count and size
- include small/incompressible/large files in compression estimate
- add a correction factor to calculations for safety margin

Change-Id: If561b0273e38e4821de228c81291859c7bb1a0d2
Test-Parameters: trivial testlist=sanity-compr env=ONLY=1007,ONLY_REPEAT=10
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53824
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>