LU-17736 tests: Fix sanityn/73 for test machines with auditd

LU-17736 tests: Fix sanityn/73 for test machines with auditd

getfattr performs one stat followed by two getxattr syscalls against
the provided file.  Normally, the stat results in no getxattr calls
internally (as it's not something stat is required to return).

However, if auditd is enabled AND one of the rules includes a
filesystem-specific rule such as watch directory X and record if it's
modified, then for every lookup (each of the three syscalls includes
one) an additional getxattr will be performed, resulting in 5 total
getxattrs.

Because there is significant fuzz here, revise the check to be
at minimum the two "expected" getxattrs but allow for more.
Comments have been added explaining this.

Signed-off-by: Ellis Wilson <elliswilson@microsoft.com>
Test-Parameters: trivial testlist=sanityn env=ONLY=73,ONLY_REPEAT=10
Change-Id: I0da5c2a5331f7dba4e65051a073e2bec05327a25
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54809
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>