deploy/ci: Fix storage issues in Ganeti

Ganeti requires at least 20G for LVM storage (yes this is a hardcoded
constant MIN_VG_SIZE). This check is done during cluster related
operations (init, modify) on all VM capable nodes.

Ganeti also checks for installed drbd module on all nodes (and NOT olny VM
capable ones; Ganeti bug to be fixed).

snf-deploy avoids these checks and initiates a cluster with
--no-lvm-storage and --no-drbd-storage. In Ganeti 2.10 these
options are removed in favor of --enabled-disk-templates.

This patch introduces a new configuration option in ganeti.conf
that reflects the Ganeti version to be installed. Currently only
two options are available; old (2.8) and new (2.10).

To deal with the storage issues, we still initialize the cluster
with only ext and file disk templates enabled, then we modify
master node with --vm-capable=no.

After each VMC setup we add the node to the cluster, and then we
cluster wide enable lvm and drbd. In the case where the master node
is a VMC as well the bug will not get triggered.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
deploy/ci: Some changes wrt disk sizes

vcluster.conf:

  disk0_size is the size of base vcluster image to debootstrap
  disk1_size if the size of the extra disk to use for LVM

ganeti.conf:

  vg_size is the size of the VG to create if an extra disk is not
found

Ganeti has a hard requirement for VG more than 20480MB.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
deploy: Add missing decorators for ExtStorage

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>