/countries/count: add integration tests

[0pdd]

The puzzle 1-d3517f90 from #1 has to be resolved:

mystamps-country/main.go

Line 12 in 7b6b288

// @todo #1 /countries/count: add integration tests

The puzzle was created by @php-coder on 04-Jan-20.

[php-coder]

We should test routing and real access to database. Let's do that in Docker containers.

Depends on #14 and #12