upgrade: fix v3ResetMetaVolSize argument

In commit c072945 (one shot prepare) the v3ResetMetaVolSize argument
was changed from volume object to volume uuid (string) triggering
attribute errors during the execution (e.g. getMetaParam, etc.).
This patch fixes the issue reintroducing the volume objects and the
relevant exception handling.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1022975
Change-Id: Iddffa996652300e5a5daa19bef5bd7873f39bb15
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20721
Reviewed-by: Dan Kenigsberg <danken@redhat.com>