Add support for specific network configuration

The networkconfig plugin can now handle custom NetworkDetails
objects that contain data like IP address, gateway, broadcast etc.

Change-Id: Ife3f8f62b47704e7f25e0304b15953d6f06e8620
Add support for OpenNebula meta-data

All the needed details are taken from a context script file
found on a ISO mounted inside the VM.

Change-Id: I2259159ea09e03e17a0c98d2fe7039f597be9190