On login cd to code dir and activate the venv

This patch also:
    * Adds a vim mode line to the Vagrantfile
    * In the Makefile pip now places its cache in /tmp
    * In the Makefile the stackwalker target now depends on the breakpad target
    * Disable timeout in puppet (pip can take a while) and log more.
    * Run vagrant_bootstrap.sh script via the Vagrant shell provisioner.
    * Adds an ignore line for the stackwalker binary that is built via the Makefile

Eventually vagrant_bootstrap.sh will just run 'setup.py install', but
for now we should have it run some essential makefile targets so that
the virtualenv works on first vagrant login.