Introduce a SharedIp object for Clustering

An io.murano.SharedIp class is added to the Core library.
This class may be used to allocate an IP address which will be later 
assigned to multiple VMs (with usage of "allowed_address_pairs") feature.
A FloatingIP address may be attached to this shared virtual address for further usage from outer world.

Also fixes an issue in NeutronNetwork which caused the net to be redeployed multiple times.

Change-Id: If821348d27c7cd8d90fe11a7f9c9fe9e0e558c03
Merge "Introduce a SharedIp object for Clustering"