match the architecture of the repo to the rest
allow branch to be overridden from the environment
clean up duplication

Renamed master_simple to master_base which can be used as a node on its own.
master and master_with_agent now inherit from that node.
update the Vagrantfile for recent changes

No longer able to pass the commit as a parameter. It could be set as an
environment variable, but given /etc/puppet is mapped to the current
directory, it doesn't serve any purpose. Allow the NODE_TYPE to be altered by
an environment variable to test a provision with master_base, for example
fix typo and permissions on add-agent-node script