ztest: if runid is set, propagate it

define test run id and make it available to ztest. This will be used to
verify we are evaluating the same test we have just built and flashed
and that we are not looking at some old output.

Existing code in ztest will use this, and twister will define the run
id.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>