Fixes #4611,#7353 - control the db_pending_migration/db_pending_seed from installer

This allows tracking the state of migration/seeding in the database
and making sure the rake tasks are done on subsequential installer attempts when
something goes wrong the first time.

Also, as part of the `foreman-config` calls, we ensure that the
settings are initialised before the httpd starts (preventing the
race-conditions happening when the httpd and rake db:seed start at the
same time)

Closes GH-225