docs(*): add DigitalOcean in a few places it was left out
docs(*): remove Rackspace support

Rackspace cannot be supported until it updates its images regularly.
Merge pull request #1364 from deis/rackspace_warning

docs(*): remove support for Rackspace
fix(controller): restart celery or gunicorn in reload script

Previously the /app/bin/reload script invoked by confd assumed that
pidfiles for celery and gunicorn always exist, which is not true in
some failure cases. This only sends them a SIGHUP if they are running,
and restarts them otherwise.

Fixes #1100.