Increase default timeout for test command.
Allow using a custom Agent with http.HttpClient.

Change tests to use an Agent with a single socket
instead http.globalAgent for consistent behavior
between node v0.10.x and v0.11.y (y >= 7):

node v0.11.4 changed
http.globalAgent.maxSockets = Inifinity (from 5)
and v0.11.7 changed the http module to only send
“Connection: keep-alive” when necessary.
Remove bad goog.require call.
Add promise support for generator functions.
Requires using harmony (node v0.11.x)