don't bind an engine to the _Model class to avoid the global scope
use more distinctive env var name for database socket
preparation to add distinct master/slave database connections
fix `/v1/search` test to match proper radio key placement
directly create test objects instead of using submit API in tests
setup sql connections to both master and slave

read-only views use the slave connection, so we can point those at the
mysql read replicas
add a simple helper script to start server for local debugging