turn path to graphlab-twill into a property

also removes "metagraph.template" from the config path. This property
is not yet being versioned in the metagraph, so it doesn't make sense
to have this reference in the property name.
Log the arguments and exit code of running graphlab-twill
Disable running branch commits in the background

The UI is not yet polling on the job status of branch creation.
So in the meantime, we'll just run it synchronously.
Merge pull request #150 from erickt/temp-fix-branches

Disable running branch commits in the background
Merge remote-tracking branch 'remotes/origin/master' into test
Merge remote-tracking branch 'remotes/erickt/twill' into test
Merge pull request #1 from erickt/test

Test