gs_cache: vendor a snapshot of chromite here

This will allow chromite to go python3-only while gs_cache is still
python2-only.  Once it gets migrated, this can be removed.

This is chromite at commit 9c919d5e0c02a9f76e441793cdc2d67b89d364ef
before ts_mon_config was converted to Python 3 only which this code
seems to rely on.

This snapshot was created by deleting all the modules & dirs that
had migrated to python3-only.  With more effort, more modules could
be deleted here, but this seems to be good enough for now.

BUG=chromium:1123908
TEST=CQ passes

Change-Id: I926379c73999e0ffcabe0c686886bf6e0c1ad977
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2736776
Reviewed-by: Congbin Guo <guocb@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
516 files changed