Fix a few minor issues

- The color for started messages for builds should be yellow
  instead of green.  This is so it is more apparent that builds
  which have not finished should be considered unstable.
- The color for non success/fail messages should be grey.
- The build message should say "Build [number]" insead of
  "#[number]".  This is so Hubot does not pick up the build numbers
  as an issue number and link to unrelated issues.