Refresh volume connections when starting instances

This patches adds network and block device information to the signature
of the power_on method on the virtualization driver. The relevant call
sites are also modified to provide the required information. The libvirt
implementation of power_on has been altered to re-establish network and
volume related connections.

Fixes bug: 1188326

Change-Id: If617b570e082e3aa321414a2680a3aa0754f6153
Merge "Refresh volume connections when starting instances"