tests: add initial tests for timeOffset handling

the handling of timeOffset has been a source of issues
recently and deserves more testing.

Change-Id: I8925945686e6dd3a6a83a87e26157aba12ec1bd3
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24252
Reviewed-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>