feat(contrib/vagrant): support multiple-VM environment

This commit modifies the Vagrantfile and Makefile in contrib/vagrant
to support an arbitrary number of Deis cluster machines.
fix(*): use host's IP address
Merge pull request #721 from opdemand/vagrant-multi-nodes

feat(contrib/vagrant): support multiple-VM environment
docs(scheduler): add and update README.md files

Fixes #705.