projectBranches function

Makes use of canBranchProject and projectBranchName (last two CLs) to
create a list of branch names for all branchable projects.

BUG=chromium:980346
TEST=run_tests.sh

Change-Id: I6f12f370cfebb513964dbc6eb5b0db01aadd93c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/go/+/1696107
Reviewed-by: Jack Neus <jackneus@google.com>
Commit-Queue: Jack Neus <jackneus@google.com>
Tested-by: Jack Neus <jackneus@google.com>
2 files changed