Change default test source root for Kotlin classes

[volivan239]

Description

When launching action on a class from Kotlin, the default test source root that is selected in UI is ../src/test/java even if ../src/test/kotlin exists.

Expected behavior

I believe that the kotlin tests source root should be selected by default in this case.

Potential alternatives

If there is no kotlin tests source root in the project, it would be nice to offer user to create it automatically (currently this isn't done, at least if there is java tests source root)

[volivan239]

Related to #786