Add openstack-common

We're going to use openstack-common to receive notifications and then
pass them via socket.io to the client.

Prerequisite for blueprint realtime-communication

Change-Id: Ic590f52f14d000d07be6ee9a8da3df976b58c302
Signed-off-by: Tomas Sedovic <tomas@sedovic.cz>
Merge "Add openstack-common"