(QA-644) Beaker vagrant backend corrupts /etc/hosts when --no-provision is passed

- add support to beaker for determining ip addresses of currently up
  vagrant hosts through reading the Vagrantfile
- if the Vagrantfile doesn't exist or ip addresses can't be determined
  then quit
adding spec tests for pulling ip addresses from existing Vagrantfile

- spec tests are good!
Merge pull request #105 from anodelman/vagrant-ip

(QA-644) Beaker vagrant backend corrupts /etc/hosts when --no-provision is passed