tdb: test for readonly locks mode on tdbbackup command

tdb: test for readonly locks mode on tdbbackup command

Simple bash test for readonly locks on tdbbackup:
1. Running tdbbackup on a database with and without readonly locks enabled.
2. Dump both backups and original.
3. Check all three dumps match.

A binary sample_tdb.tdb file is included for the test because the existing
sample tdbs in lib/tdb/test are either corrupt or empty.

Signed-off-by: Aaron Haslett <aaron.haslett@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>