enable_internal_db script updates

- Uses the new `interactive` param from this PR: https://github.com/ManageIQ/cfme/pull/1246

https://github.com/ManageIQ/cfme/pull/1246
README updates

- Also removed the path-munging code to add cfme_pages to the python path
  since the README now leaves it to the individual developer to set use
  the PYTHONPATH env var
Merge pull request #166 from seandst/readme-updates

README updates
Merge pull request #164 from seandst/enable-internal-db

enable_internal_db script updates
External DB listener test

- Goes a little bit beyond just making sure 5432 is open and
  also sanity-checks the miq_databases table
Merge pull request #171 from seandst/test-appliance-db

External DB listener test