CountryServiceImpl.findIdsByNames(): add unit test for converting to lower case

[0pdd]

The puzzle 819-5c89f089 from #819 has to be resolved:

mystamps/src/main/java/ru/mystamps/web/service/CountryServiceImpl.java

Line 85 in 0c32c0e

// @todo #819 CountryServiceImpl.findIdsByNames(): add unit test for converting to lower case

The puzzle was created by Slava Semushin on 20-Jan-18.