llvm_tools: teach patch updating logic about google3-unstable

This CL lets us use the new google3-unstable option from
update_chromeos_llvm_next_hash.py. It also includes some formatting
changes forced by `yapf`.

BUG=chromium:914081
TEST=Unittests have no new failures; ran the script with
     google3-unstable, and it appeared to parse.

Change-Id: Ib70e238b383e91dfa7c7df04d716e7127402f68a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/1793907
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
2 files changed