Revert "Force vdsm to stay with libvirt <= 1.2.7"

This breaks live merge and is not needed now.

This reverts commit 4573eca868c7d13f36265bbe4901b4f2716311e3.

Change-Id: Iffa726906cc8fe4f8ba7f5be377a51d19ee46078
Signed-off-by: Martin Sivak <msivak@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32786
Reviewed-by: Dan Kenigsberg <danken@redhat.com>