fix: changed the public/private_ip_of methods on silverware node_utils to be less likely to return nil

Squashed commit of the following:

    fix: changed the public/private_ip_of methods on node_utils to be less likely to return nil

commit 6d3d66cd493bc179dcae7244e1e945ca3d3f404f
Author: Chris Howe <howech@infochimps.com>
Date:   Wed Feb 19 14:34:22 2014 -0600

    Change-Id: I68c51373e0a9d4966acd1287a1a2419255a27832

Change-Id: If750ab2ff1190bd10b8821c9311b112fa48d91f2
Merge "fix: changed the public/private_ip_of methods on silverware node_utils to be less likely to return nil"