Include commit 'sha' in pull request status file

The file containing which pull requests have previously been seen was
extended to include the commit 'sha', in addition to the pull request
number. This allows the script to differentiate between pull requests
that have been updated since it was last seen, and pull requests that
have not been updated. Any updated pull requests should be re-run
through the testing infrastructure.

In addition, this change adds the '--repository' option to the command
used to submit a new change to the buildbot instance.

Signed-off-by: Prakash Surya <surya1@llnl.gov>