Added defaults for different device functions, spines, leaves, exit and oob-switch default to 300MB Vx images, hosts, and oob-servers default to 500MB ubuntu1604 images
Added defaults for different device functions, spines, leaves, exit and oob-switch default to 300MB Vx images, hosts, and oob-servers default to 500MB ubuntu1604 images

linuxsimba/topology_converter,linuxsimba/topology_converter