LU-17777 tests: Exclude Files when comparing dir structure

LU-17777 tests: Exclude Files when comparing dir structure

This patch Excludes /etc/yum* and /etc/pki* as corner case
which is updated by RHEL asynchronously breaking the test-case.

Moves search folder from "/etc /bin" to "/etc /usr/bin" as
/bin can be a symlink

Removes arbitrary return code of 18 and 22 with $?. For
diff this should be 1 for mismatch and 2 for files not found

Renames constant error message with unique message when
rebuilding dir structure before and after remount

Test-Parameters: trivial testlist=runtests
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I8f7824b930f6286e7e5744ff403a02cec280075d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58129
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Deiter <adeiter@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>