The update_scripts step doesn't set '--reset'
Additionally, if there was no fetch config, don't fail trying to unset it.

Tbr: agable@chromium.org
No-Try: True
Bug: 862547
Change-Id: I90886ca7d1dd20ae59b378a5998de47dc67c60f9
Reviewed-on: https://chromium-review.googlesource.com/1137693
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>