Load only the Job columns we need in JobController
Use load_only() to speed up Job checking
Update indexes

Remove some indexes and add others to improve performance. Include
alembic migration.
Use load_only to speed up Node checking

Also use a try/except block around a NoResultFound exception instead of
calling count(), since that's slow on PostgreSQL
Use load_only() in NodeController.__init__()
Index Node.name
Fix broken test
Add a new test: test_job_adds_node()
Make Job.target_nodes load dynamically

Also use load_only() when checking self.target_nodes and include a unit
test to make sure we're not breaking things.
Index both columns in job_nodes