Add more disk/nic listing options in gnt-instance
Add more disk/nic listing options in gnt-instance

This adds some more listing cases (useful for scripting/rapi):
  - disk.sizes for a list of all sizes
  - nic.(ips|macs|bridges)

Reviewed-by: imsnah

dimara/ganeti,onponomarev/ganeti,ganeti/ganeti,yiannist/ganeti,grnet/snf-ganeti,andir/ganeti,bitemyapp/ganeti,apyrgio/ganeti,leshchevds/ganeti,ganeti/ganeti,dimara/ganeti,leshchevds/ganeti,andir/ganeti,grnet/snf-ganeti,leshchevds/ganeti,bitemyapp/ganeti,mbakke/ganeti,mbakke/ganeti,ganeti/ganeti,onponomarev/ganeti,apyrgio/snf-ganeti,apyrgio/snf-ganeti,mbakke/ganeti,yiannist/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/ganeti,andir/ganeti,ganeti-github-testing/ganeti-test-1