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
(cherry picked from commit 7331c71e0cd7376a14a912924ee23aaecaa8f34f)