And use that when constructing log paths and URLs. Use a substr
of the change id or commit sha when constructing URLs so the log
directories are deeper.
Make copying the test results a macro (it's used in several places).
Update the gearman log client to take advantage of the new parameter.
Requires https://review.openstack.org/#/c/36304/
Change-Id: I64faa35eddc4105271efa3de4f83b608b77655c2