EX-7795 scripts: add whole file to compression scan

EX-7795 scripts: add whole file to compression scan

Add a mode where the compression scan script compresses the
entire file, which in theory should 100% match the
compression results from using CSDC and allow a test to
calculate the exact space usage reduction expected by
using CSDC.

This is intended to be used mostly for testing.

Change help documentation slightly to make clear this can
also accept a path to a single file.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I606a33d686d87dd631bf5b33dc85ee8c24fe9f67
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52406
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>