When you have `libpam-devel` installed, PAM support in teleport gets
enabled. But when you didn't run `make -C build.assets/pam install`, the
configuration that `lib/pam` tests rely on is not in place.
This causes test failures which may be confusing for newcomers who
happen to have `libpam-devel` installed.
Manually check that all services and `pam_teleport.so` are installed
before running the tests, to avoid annoying failures.
Also, refactor PAM tests to the new style.