Add python to Depends in debian/control.

Apparently it must be explicitly reported, otherwise lintian complains with:
E: globaleaks: python-script-but-no-python-dep usr/bin/gl-admin
E: globaleaks: python-script-but-no-python-dep usr/bin/globaleaks

(thought that python-dev was just fine as well).
Ignore appliances output-* directories in dpkg-source.

This way, you can build a sane debian package while building a vagrant machine.
Remove scripts/travis directory - #1046.