core: Add migration options to OVF

Most migration options were not saved in OVF, this caused a problem when
changing those options while VM was running (due to the "next run" snapshot OVF).

- Added support for the options: MIGRATION_SUPPORT, DEDICATED_VM_FOR_VDS
  and USE_HOST_CPU in the OVF reader\writer.
- Added verification for the DEDICATED_VM_FOR_VDS option - makes sure host
  exists in the current  cluster. Added in: import vm, import template,
snapshot manager.

Change-Id: I5f0025e5ac59dac0a1569729c2fef8186e0885db
Bug-Url: https://bugzilla.redhat.com/1124449
Signed-off-by: Eldan Shachar <eshachar@redhat.com>