Bug 1028407 - Establish connection to server faster; r=jgriffin

There was a 5 second sleep() in the Marionette client that made
establishing connections to servers take a long time. The history of
this value is unclear, but bug comments seem to indicate that Gecko
wasn't completely initialized during the observer notification that
starts the server.

We insert some code to let the JavaScript event loop spin for a few
ticks before starting the Marionette server. This should hopefully give
Gecko enough time to initialize.

--HG--
extra : rebase_source : e1b4533a4c77d1b250ff178d4a2b28ad78ffe764
extra : histedit_source : ba1d1be17d6c57c06910eac369811180db2abba6