Automatically Create and Migrate Test Databases on Linux

[HCLarsen]

On Linux, when running specs in an Amber app, no test database is created or migrated, resulting in an error of a missing database. Since the commands of amber db create and amber db migrate only create and migrate the development database, the current workflow requires manually creating and migrating the test database separately.

To speed up the workflow, it would be beneficial to having the creation and migration of test databases happen automatically, either when running the commands for the development database, or when running the specs.