Add get_my_ip()

At the moment function _get_my_ip() exists (at least) in Cinder,
Ironic, Neutron, Nova and Tuskar, so there is a sense to keep
it in common code.

Change-Id: I3c37d6ea3e8bef7b8a5e21baedd1b2b94369515f
Merge "Add get_my_ip()"