Fix is_trybot for no-buildbot bots

Fix is_trybot for no-buildbot bots

This was breaking gold/perf trybot results for no-buildbot bots.
Note that:
- Upload destination was correct, due to upload_nano_results using the
  correct property names.
- Patches were properly applied, since bot_update uses the properties
  independently of our logic.

BUG=skia:

Change-Id: I16f2e2d24d4602dc73233784d098f00b745e061a
Reviewed-on: https://skia-review.googlesource.com/5201
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Eric Boren <borenet@google.com>