Add AD DC performance tests

Add AD DC performance tests

These test a variety of simple AD DC operations.

These tests are NOT independent of each other and must be run in the
right order (alphabetically, which is guaranteed by Python's unittest
module) -- the running of each test is part of the set-up for later
modules. This means we have to subvert unittest a bit, but it saves
hours of repeated set-up.

These tests are not intended to push edge cases, but to hammer common
operations that should work on all versions of Samba. The tests have
been tested back to Samba 4.0.26.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>