[qa] Avoid race in preciousblock test.

If node 0 is sufficiently fast to announce its block to node 1,
node 1 might already have the block by the time the
node_sync_via_rpc loop gets around to node 1, resulting in the
submitblock result "duplicate-inconclusive" as node 1 has the block,
but prefers an alternate chain.

qa/rpc-tests/preciousblock.py

@@ -102,7 +102,7 @@ class PreciousTest(BitcoinTestFramework):
         assert_equal(self.nodes[2].getblockcount(), 6)
         hashL = self.nodes[2].getbestblockhash()
         print("Connect nodes and check no reorg occurs")
-        node_sync_via_rpc(self.nodes[0:3])
+        node_sync_via_rpc(self.nodes[1:3])
         connect_nodes_bi(self.nodes,1,2)
         connect_nodes_bi(self.nodes,0,2)
         assert_equal(self.nodes[0].getbestblockhash(), hashH)