Miscellaneous Postgresql Fixes to Formula, gunicorn Worker Timeout by Default

[p6knewman]

Hi!

Loving alcali so far and appreciate you open-sourcing this! We're using a postgres backend and ran into a few minor issues with the formula. Also frequently ran into worker timeouts when refreshing our 200 or so minions in this environment. Thoughts on this PR?

• Changing db_backend for PGSQL from postgres->postgresql to match the name of the Django DB backend name
• Setting a higher default gunicorn worker timeout. Seeing the 30s default get hit regularly when using only 200 or so minions
• Adding worker_timeout to systemd unit

Jun 25 13:54:37 svlchi6dsalt1 alcali[12269]: django.core.exceptions.ImproperlyConfigured: 'django.db.backends.postgres' isn't an available database backend.
Jun 25 13:54:37 svlchi6dsalt1 alcali[12269]: Try using 'django.db.backends.XXX', where XXX is one of:
Jun 25 13:54:37 svlchi6dsalt1 alcali[12269]:     'mysql', 'oracle', 'postgresql', 'sqlite3'