Handle the default leapp-test repository better

[danmyway]

Is your feature request related to a problem? Please describe.
The default setting for test repository location is github.com/oamg/*
When testing leapp-repository the default reponame is leapp-tests which results in a weird and faulty behaviour when -g gitlab.cee.redhat oamg leapp-tests is not specified.
That resolves to github.com/oamg/leapp-tests and the resolution of that fails as the repository doesn't exist.

Describe the solution you'd like
Set a default value for the repository location when testing leapp-repository to the correct value.

Additional context
Add any other context or screenshots about the feature request here.

[github-actions]

Hi, there.

Thank you @danmyway for suggesting this. Someone will take a look at this shortly.

---

This is an automated comment created by the peaceiris/actions-label-commenter. Responding to the bot or mentioning it won't have any effect.