a new repository location class.

GITLAB_USERNAME and GITLAB_PASSWORD may be specified for an LDAP login, but QA
scenarios may need to know which type it is in order to log in successfully.

Signed-off-by: Rémy Coutable <remy@rymai.me>

We call it for a second time in EE.

For added confidence, and because I plan to fiddle with some behaviours
shortly, add spec testing to the newly extracted
QA::Scenario::Entrypoint class.

[ci skip]