Bug 516407 Set Agent and make package.json downloads more robust

The ESP8266 URL started reject connections. Turns out setting the
User-Agent property on the connection fixes that. I also made this
more robust from download failures so that at least other packages
can be downloaded. Finally, I removed the ESP8266 URL from the
defaults.

Change-Id: Ib2ea5667ba490ae660883a30b3049c3d736cfdb7
2 files changed