[environment/base] Move puppetfile to base environment

All current environment implementations support Puppetfiles and that's
unlikely to change, so the puppetfile attr_reader and creation can be
pushed into the base class.
[environment/base] Define abstract #status method
[environment/git] Implement #status method
[environment/svn] Implement #status method
Merge pull request #230 from adrienthebo/feature/master/environment-status

environment: push Puppetfile into base class, add #status