Update source /bin/agent commands to function like deb & redhat versions

Fixes issue #512, where running any source agent command (status, info, etc.) would start supervisor.

Also updated the source status command to return 1 if the agent is not running, and updated it to check that the correct processes are actually running.

Finally, I updated start, stop, and restart to check if the supervisor is running before executing. Also, now if the commands fail they will also exit with a non-zero exit code.

All of these changes bring the source agent commands more in-line with the Red Hat and Debian agent commands.