LxcProvider network refactoring

Tunnels are used for ip connectivity between nodes. This makes
possible to use LxcProvider in any environment, and deploy
clouds with huge number of nodes.

Class LxcContainer has been replaced by more convenient LxcHost.

Added new exception ConfigValidationError.

blueprint multihost-deploy

Change-Id: Iff287468535afc0840d4d233bf393c7ddf02b911