add libvirt_domain_type option

Specify the domain type via the config file to support different
hypervisors. Also adds sane config defaults in case they're not
specified in the config file.
Fix pep8 errors
Replace Cheetah templating engine
Simplify tox env
Fix pylint errors
Return extended server details after booting

Otherwise the latest 'nova boot' command will complain:
ERROR: 'NoneType' object has no attribute 'get'