Run post cluster initialization LU

Call PostInitCluster from 'gnt-cluster init'.

Signed-off-by: Luca Bigliardi <shammash@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

scripts/gnt-cluster

@@ -92,6 +92,8 @@ def InitCluster(opts, args):
                         candidate_pool_size=opts.candidate_pool_size,
                         modify_etc_hosts=opts.modify_etc_hosts,
                         )
+  op = opcodes.OpPostInitCluster()
+  SubmitOpCode(op)
   return 0