(PDB-4636) services: defer db pool inits until needed
(PDB-4636) services: defer db pool inits until needed

Particularly so that we don't have to worry about attempting
migration checks until after the db has ben initialized.

puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb