EX-6510 csdc: prefer uncompressed mirror for write

EX-6510 csdc: prefer uncompressed mirror for write

When writing to mirrored files with both compressed and uncompressed
mirrors, prefer the uncompressed components to write, and that is
better for performance, more compatible with older clients, and better
fits the model of compressing files after initial write.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I62a117d5cc3d34e2c0c96d1a9ade8eef0a2d1291
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/50974
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>