EX-7596 tests: disable metadata_csum_seed for pcc cache device

EX-7596 tests: disable metadata_csum_seed for pcc cache device

latest e2fsprogs enable metadata_csum_seed feature when mkfs.ext4
a device, which is used in pcc test as a cache device. Such a ext4
fs cannot be mounted on an old kernel of el7. So disable this
feature for pcc cache device if it is detected in sanity-pcc test.

Signed-off-by: Lei Feng <flei@whamcloud.com>
Test-Parameters: trivial testlist=sanity-pcc clientdistro=el7.9
Change-Id: I2ef3ff27b49fb479ec348b742cf614a43321813b
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51234
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>