'Adds a virtual disk to the specified VM or VMs under the vApp. If the
vapp_or_vm_id param represents a link to an vApp all VMs that are
attached to this vApp will be modified.
:keyword    vapp_or_vm_id: vApp or VM ID that will be modified. If a
vApp ID is used here all attached VMs
will be modified
:type       vapp_or_vm_id: ``str``
:keyword    vm_disk_size: the disk capacity in GB that will be added
to the specified VM or VMs
:type       vm_disk_size: ``int``
:rtype: ``None``'

def ex_add_vm_disk(self, vapp_or_vm_id, vm_disk_size):

    self._validate_vm_disk_size(vm_disk_size)
    self._add_vm_disk(vapp_or_vm_id, vm_disk_size)
