Update sqerl config to use db_driver_mod

The old setting was deprecated and throwing warnings on erchef start,
but erchef was just using the default (and only option) of postgres,
so everything was still working.
Add sqerl idle check config

This overrides the default (default is 1000) making it instead
10000. This causes the idle check to happen less often, conserving
CPU on the chef server when it is idle.
Merge branch 'mm/update-sqerl-configs'