selftest: add an expectedfail directory

selftest: add an expectedfail directory

We have some tests that are not only known to fail, but which are
intended to fail.

For example, to quote selftest/knownfail.d/dns:

> # These tests are expected to fail because we want to ensure that
> # unauthenticated updates are not permitted against the default
> # configuration, nor against an RODC

In contrast to selftest/knownfail.d/uac_objectclass_restrict, which
says:

> # All these tests need to be fixed and the entries here removed

That one should stay in selftest/knownfail.d.

Some files are mixed. For example, there are lines in
selftest/knownfail.d/smb1-tests which were added in *commits* that say

> We also need to add a knownfail (which will not be removed) for the
> new test which will fail in smb1 envs

but it is not clear to me that the whole file is expected to always
fail.

By moving some knownfails here, we allow selftest/knownfail.d to be a
bit more like a TODO list, containing things that actually constitute
failure.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>