Update test suite and apt-mirror to take into account that we're building releases from the checked out tag nowadays.

We'll need it to replace special chars in tagged APT snapshots names,
in apt-mirror.

Fix-committed: #11403

This might improve reliability somewhat. At least we depend on one
less host being up (we already depend on our website).

Refs: #10442

Fix-committed: #11123

We already depend on our website working so that is fine, but this way
we don't depend on html5.org working, which it wasn't a few minutes
ago.

This will not be the final 6.0, hence including the -build1 to
distinguish from the final 6.0 that we'll upload closer to 2016-06-07
(when Tails 2.4 is planned, and when the ESR Tor Browser 6.0 final
will be based on is officially released).

It might be that
https://jenkins.tails.boum.org/view/RM/job/test_Tails_ISO_devel/351/ would have
succeeded if we had given it a little bit more time.