tests: Abstract the docker image tag for Weekly tests

This abstraction allows us to more easily change the tags between
different gem5 releases and/or between stable and the develop branch.

Change-Id: Iad49cabac9b4000e8570162d3e12453c6d097ee2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65921
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed