fix(github): update URL references to opdemand/deis

Refs #711.
Merge pull request #801 from deis/deis-deis-fixup

fix(github): update URL references to opdemand/deis
refactor(Vagrantfile): merge Vagrantfiles and update to upstream

This commit merges the Makefiles and Vagrantfiles, and supports
both a 1-node and n-node local cluster with the same files. Also,
the user-data and override-plugin have been updated to be more
closely in line with upstream. Also updates README with additional
instructions.

closes #760, #747