framework: Add feature to mark workloads unsafe for confidential devices

Some workloads, such as Geekbench, may phone home and report data about the
device they are running on. This poses a risk for users that are testing on
unreleased or otherwise confidential devices - perhaps they use a standard
agenda to run a large battery of tests, in which case they may forget to disable
these dangerous workloads.

This provides a mechanism to prevent running those workloads from running by
setting allow_phone_home=False in the user configuration.

wa/framework/execution.py

@@ -411,6 +411,13 @@ class Runner(object):
             self.check_job(job)
 
     def do_run_job(self, job, context):
+        rc = self.context.cm.run_config
+        if job.workload.phones_home and not rc.allow_phone_home:
+            self.logger.warning('Skipping job {} ({}) due to allow_phone_home=False'
+                                .format(job.id, job.workload.name))
+            job.set_status(Status.SKIPPED)
+            return
+
         job.set_status(Status.RUNNING)
         self.send(signal.JOB_STARTED)