Fixes related to mutl-domain deployments

Now the external-domain-checker returns a list of local domains that can be reused between calls of ChannelManager.isLocalDomain(), ChannelManager.isLocalJid() or ChannelManager.isLocalNode(). 
It drastically improves the perfomance of disco#items, purging remote cache, etc,... and allows for a selective query of local nodes.

Since HSQLDB is not fully compliant with postgres, I had to Mockito.spy the SQL connection object in the tests in order to replace **~** with **regexp_matches**.
It helps solving the performance issues we currently have. In cases we need to check if a lot of nodes are local - for example, in a for loop - we just need to execute the local-domain-checker once, and then pass this list around.