Fix test groups vcenter_one_node_simple and vcenter_ha

There is ostf test 'Launch instance, create snapshot, launch instance from
snapshot' which never works in Fuel 5.x with vCenter hypervisor due to
timeout problem. And in system tests vcenter_one_node_simple and vcenter_ha it
was marked as 'should fail'.

Now problem with timeouts solved (see https://review.openstack.org/#/c/138744/)
and mark 'should fail' must be canceled.

Closes-bug: 1401846
Change-Id: Idc63dea0c32fcc471629b10a07a09fb3ecce9d2d
Merge "Fix test groups vcenter_one_node_simple and vcenter_ha"