Bug 1419180 - [taskgraph] Stop implicitly scheduling 'when.files-changed' tasks if taskcluster/taskgraph is modified, r=dustin

This only affects the lint and python-test tasks which have the 'always_target'
config set.

This behaviour hasn't proven very useful, largely because when modifying
taskcluster/taskgraph, a lint task (f8) and a python task (tg) get scheduled
anyway. Running the other lint and python tasks in addition doesn't add much
test coverage and only serves to increase noise and waste resources.

MozReview-Commit-ID: LTWyK03UoNY

--HG--
extra : rebase_source : 15f8dcdf5016e44b31065f37fa79dc730f448f79

taskcluster/taskgraph/transforms/job/__init__.py

@@ -115,11 +115,8 @@ def rewrite_when_to_optimization(config, jobs):
 
         files_changed = when.get('files-changed')
 
-        # add some common files
-        files_changed.extend([
-            '{}/**'.format(config.path),
-            'taskcluster/taskgraph/**',
-        ])
+        # implicitly add config directories affecting task
+        files_changed.append('{}/**'.format(config.path))
         if 'in-tree' in job.get('worker', {}).get('docker-image', {}):
             files_changed.append('taskcluster/docker/{}/**'.format(
                 job['worker']['docker-image']['in-tree']))