repopick: gracefully handle empty/non-JSON server responses

Change-Id: Idbabdbfb4a910de0ad405f02b2a84cf2bc9ef3dc
repopick: remove the superfluous information from date

  * '2011-11-17 06:54:52.000000000' -> '2011-11-17 06:54:52'

Change-Id: I73d37c9aba13d4be6b4d2d2fc0f2f83971a3e77b
repopick: let's be nice to our servers :)

* Prefer fetching changes from GitHub, and if that fails,
  silently fall-back to Gerrit.

Change-Id: Ibf68d4b69a7e8dbee2adb8f7f4250340b8be629c
Merge remote-tracking branch 'cm/cm-10.1'