`make test` ignores `DATABASE` and `SOURCE` variables

[morigs]

Describe the Bug CONTRIBUTING.md mentions that it's possible to run tests for specific database only by providing DATABASE variable.

However, the DATABASE_TEST variable is not used anywhere in the Makefile, so it runs all existing tests. The same for SOURCE variable. The reason is - TEST_FLAGS variable is empty.

Steps to Reproduce Steps to reproduce the behavior:

1. make test-short SOURCE='file go_bindata' DATABASE='postgres'
2. Tests for other databases are running

Expected Behavior Only tests for postgres are running

Additional context Possible solution: replace ./... with the list of database tests paths and fill TEST_FLAGS with --run flags