Update Travis CI documentation

We've moved from the cron job triggering of the update-git.sh script to
our public Jenkins server, so updating the documentation accordingly.

Tracked in https://trello.com/card/update-travis-md-with-info-about-ci-opensuse-org/50809fb54fa7ad9c1a000f4d/137
Fix feature/grizzly release metadata
Fix up how the CI system finds valid next builds.
Fix up ci_all_next_states to keep up with changes elsewhere.

Fix glitch in ci_register_intent that was only allowing one next state
to be chosen.
Handle special-case of a zero-time intent.
include comment showing how to create admin node