engine: Initialize array 'imageParameters' in VdcActionParametersBase

Currently this non initialized array causes NullPointerException when
trying to create VM from Template without disks.

Change-Id: I0fdaf131ed3d1bbfadcdd60df3feb6b828c05d0c
Bug-Url: https://bugzilla.redhat.com/1000789
Signed-off-by: Sergey Gotliv <sgotliv@redhat.com>