When using non-squashed uploads, there usually isn't an associated
issue with a branch. Thus setting WIP when the issue tag wasn't
present would continually set WIP even on trivial rebases. Not
adding the WIP tag when uploading allows the user to set WIP manually,
while not forcing the WIP flag after every new upload.

Also updates the unit tests that use no-squash.

Bug: 767439
Change-Id: I990a82139fefe1a0c5c7b149d39045cf985539b7
Reviewed-on: https://chromium-review.googlesource.com/1033187
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>