vagrent: fix numbering in README

To avoid breaking the list numbering, the paragraph must be indented.
vagrant: use verbatim blocks for commands

Inline monoespace text was used before -- a proper verbatim block
looks nicer with proper padding and takes up the full line width.
vagrant: simplify here document in bootstrap

Using cat, we can write to the files directly.
vagrant: make Git use https:// URLs (fixes #170)
vagrant: install Swift Browser in VM

This will install Swift Browser in a container named 'swift-browser'
and show the URL to the user.
vagrant: use commands compatible with Vagrant 1.4.3

Vagrant 1.6 introduced the "Vagrant Cloud" and that version of Vagrant
knows to look for missing boxes there.

Earlier versions did not have this feature, so for them we explicitly
add the box before running 'vagrant up'. This is for course also
compatible with newer versions of Vagrant.
vagrant: make vagrant download box as needed

This works with Vagrant 1.4.3.
tox: set Python version to 2.7

On my Debian testing system, tox attempted to run the tests with
Python 3.4 before. It now uses Python 2.7 and the tests work.
Merge pull request #171 from mgeisler/vagrant

vagrant: Install Swift Browser in VM