Add a tempestrunrc for configuring run-tempest

Add a tempestrunrc file which is sourced by run-tempest
to get input settings such as image-name and concurrency.

Variables in tempestrunrc can be via the ExtraConfig of
the image where the element is deployed.

Change-Id: I24b04b22e911732ffb9884a15cc45afabc02100a
Merge "Add a tempestrunrc for configuring run-tempest"