See https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Ftryserver.chromium.android%2Fandroid_n5x_swarming_rel%2F34660%2F%2B%2Frecipes%2Fstderr for an example

  File "/b/.remote_run_cipd/recipe_engine/fetch.py", line 193, in checkout
    recipes_cfg_text = base64.b64decode(recipes_cfg_request.text)
  File "/usr/lib/python2.7/base64.py", line 73, in b64decode
    return binascii.a2b_base64(s)
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2019' in position 1467: ordinal not in range(128)

Exception above. This really shouldn't be happening; somehow requests is giving us some weird stuff, it looks like.

We should add some logging about these errors, and try to figure out what exactly is causing this error.