xfstests: check if qa user can execute commands

_require_user only checks if the qa user exists in /etc/passwd. It may exist
though still not be able to execute anything (e.g. with a /bin/false shell).

_user_do cannot determine failure to execute the given command, as it uses
_user_do_filter for post-processing which succeeds even if the command
fails. Thus, the check should be performed by _require_user.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>

common.rc

@@ -933,6 +933,8 @@ _require_user()
     qa_user=fsgqa
     _cat_passwd | grep -q $qa_user
     [ "$?" == "0" ] || _notrun "$qa_user user not defined."
+    echo /bin/true | su $qa_user
+    [ "$?" == "0" ] || _notrun "$qa_user cannot execute commands."
 }
 
 _filter_user_do()