The SCMClient unit tests have been using an old OptionsStub in

rbtools.tests (the only thing in that module) to define default

options for a while. This hasn't been kept up-to-date, missing a lot of

defaults that specific tests have had to provide. It also doesn't play

well with type annotations, and isn't worth fixing to do so.
SCMClientTestCase now supports default options that are used in calls

to build_client(). There are set of global defaults

(DEFAULT_SCMCLIENT_OPTIONS) that will always be applied, and a

per-suite set of defaults (default_scmclient_options) that can be set.
These can then be overridden via build_client() as before.
OptionsStub is no longer being used, and will emit a deprecation

warning. We'll remove it in 5.0.

All unit tests pass.