Fix matches_local file verifier when used with sudo

Before:

    $ sudo touch /root/my_file.txt
    $ sudo [ "X$(md5sum /root/my_file.txt|cut -d\  -f 1)" = "Xd41d8cd98f00b204e9800998ecf8427e" ]
    md5sum: /root/my_file.txt: Permission denied

After:

    $ sudo touch /root/my_file.txt
    $ sudo bash -c '[ "X$(md5sum /root/my_file.txt|cut -d\  -f 1)" = "Xd41d8cd98f00b204e9800998ecf8427e" ]'
    $ echo $?
    0