tests: reenable basic auth test and add @ in username

tests: reenable basic auth test and add @ in username

On launchpad #1558484 a user reports that @ in the authentication tokens
parsing of sources.list isn't working in an older (precise) version. It
isn't the recommended way of specifying passwords and co (auth.conf is),
but we can at least test for regressions (and in this case test at all…
who was that "clever" boy disabling a test with exit……… oh, nevermind.

Git-Dch: Ignore