framework: set context for loggers

Set context for the loggers of the Runner, the workloads and the
installed instruments and processors. Errors/warnings logged by these
entities will be automatically added as events.

wa/framework/job.py

@@ -57,6 +57,7 @@ class Job(object):
     def initialize(self, context):
         self.logger.info('Initializing job {} [{}]'.format(self.id, self.iteration))
         with signal.wrap('WORKLOAD_INITIALIZED', self, context):
+            self.workload.logger.context = context
             self.workload.initialize(context)
         self.set_status(Status.PENDING)
         context.update_job_state(self)