Bug 1602863 - migrate linux32/opt web-platform-tests to ubuntu1804 r=…

…jmaher

Changes:

Because part of the setup for `test-linux` jobs are done in `taskcluster/taskgraph/transforms/tests.py`, I suspect there isn't an easy way like in `test-macosx1014` to migrate a green suite one at a time, in piecemeal fashion.

This is the alternative proof of concept:

- rename the linux jobs with treeherder/job labels that include the version number like every other platform on our CI
- like `test-macosx1014`, create two test sets in `test-sets.yml` and stop running tests that are green on the older platform. If test has issues running on the new platform, keep it on the older, green platform at the moment while issues are worked out.

As proof of concept, apply this to `linux32/opt web-platform-tests` tasks

Differential Revision: https://phabricator.services.mozilla.com/D58025

--HG--
extra : moz-landing-system : lando

taskcluster/ci/test/test-platforms.yml

@@ -19,7 +19,7 @@
 ##
 # Linux platforms (matching /linux.*/)
 
-linux32-shippable/opt:
+linux1804-32-shippable/opt:
     build-platform: linux-shippable/opt
     test-sets:
         - linux32-tests

taskcluster/taskgraph/transforms/tests.py

@@ -571,7 +571,10 @@ def set_defaults(config, tests):
         test.setdefault('loopback-audio', False)
         test.setdefault('loopback-video', False)
         test.setdefault('limit-platforms', [])
-        if config.params['try_task_config'].get('ubuntu-bionic'):
+        # Bug 1602863 - temporarily in place while ubuntu1604 and ubuntu1804
+        # both exist in the CI.
+        if ('linux1804' in test['test-platform'] or
+                config.params['try_task_config'].get('ubuntu-bionic')):
             test.setdefault('docker-image', {'in-tree': 'ubuntu1804-test'})
         else:
             test.setdefault('docker-image', {'in-tree': 'desktop1604-test'})