Script for controlling providers from the command line

Also added support scripts:
- utils/credentials.py, analogous to utils/cfme_data.py
  (in fact, a copypasta)
- providers utils to help mix in cfme_data and credentials knowledge to
  get a provider instance based on cfme_data name alone
Merge pull request #135 from seandst/provider-tools

Script for controlling providers from the command line