Move config-related code out of cloudenvy.core
Catch novaclient BadRequest on secgroup conflict

1) This exception should not be caught in the core API
2) This change paves the way for alternate cloud APIs
Move server deletion into cloud API
Load cloud APIs from entry point
Drop get_image CloudAPI method
Add EC2 cloud API
Move openstack-specific config validation out of core
Move openstack-specific build_server kwarg out of core
Move is_server_active check into cloud APIs
Move network-ready check to cloud APIs
Reword server/network not ready messages
Move network creation to cloud APIs
squash! network move
Make floating IP commands specific to openstack cloud API