Finish Internal api quicktests

[nil0x42]

the tests/core/internal-api test suite has been refactored and completed, in order to test all internal api functions correctly.

just a little hack: cleanup_login_records() is not tested, because testing it cannot really be done outside of functional tests.

[ghost]

And there I was, banging my head on the desk wondering how to tackle cleanup_login_records(). I will add a commit removing open() checks. @chqrly will be able to merge after that.

[nil0x42]

okay, i tried chroot, but openpty also requires /dev/pts to succeed, if anything fails our own utmp/wtmp files can be impacted, this is a pain for the ass,

only reliably testable through functional tests

[ghost]

Everything is looking good. Merging.

[nil0x42]

okay