runner_core.py: treat mlab-ns like rendezvous

When mlab-ns or rendezvous terminate, we don't need to detach
the streaming logger, because the test is indeed beginning.

Fixes the problem with the dash test that stops after four
seconds when run on the command line, which was reported
by Antonio a couple of days ago.
mod_dash: print the server address at INFO level

Simplifies first-cut debugging without forcing one to re-run
the test with -v.

Difficulty spotted and reported by Antonio Servetti.
Neubot/0.4.16.9 released
scripts/sign_all: remove code to sign an mlab release

Now the mlab release process is completely different and there
is no need to sign the mlab tarball anymore.
updater_runner.py: only print the signature in debug mode

The signature in base64 is too long and screws up the logs
view in the web user interface.

Given that the signature is a detail, which is not that
interesting to the average user, print the signature only
when we are running in debug mode.
Merge branch 'stable'