LU-2930 test: add tests for data version

This patch adds support of dataversion access in
multiop and use it to test dataversion on volatile
file.
It also adds a test in sanity.sh to validate dataversion works as
expected (changes between writes)

Signed-off-by: JC Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Change-Id: I62c2b2124d225331873185d92f5c2404a74b1196
Reviewed-on: http://review.whamcloud.com/5660
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>