tc-testing: split config file

Move the config customization into a site-local file
tdc_config_local.py, so that updates of the tdc test
software does not require hand-editing of the config.
This patch includes a template for the site-local
customization file.

In addition, this makes it easy to revert to a stock
tdc environment for testing the test framework and/or
the core tests.

Also it makes it harder for any custom config to be
submitted back to the kernel tdc.

Signed-off-by: Brenda J. Butler <bjb@mojatatu.com>
Acked-by: Lucas Bates <lucasb@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>