Decode stdout from ansible-playbook before logging

We log ansible parse errors specially, but the current loop
produces a bunch of lines with b'' which isn't as nice looking
as it should be.

Change-Id: I3e62e6a938422ee02099b2dfe3e1350311c722b4

zuul/executor/server.py

@@ -1617,7 +1617,8 @@ class AnsibleJob(object):
                     now=datetime.datetime.now()))
                 for line in syntax_buffer:
                     job_output.write("{now} | {line}\n".format(
-                        now=datetime.datetime.now(), line=line))
+                        now=datetime.datetime.now(),
+                        line=line.decode('utf-8').rstrip()))
 
         return (self.RESULT_NORMAL, ret)