QA: stop nodes after RPC tests, even with --nocleanup

`--nocleanup` should provide a way to preserve test data, but should not have an impact on whether nodes are to be stopped after the test execution.

In particular, when currently running RPC tests with `--nocleanup`, then it may result in several active `bitcoind` processes, which are not terminated properly.

qa/rpc-tests/test_framework.py

@@ -128,10 +128,12 @@ class BitcoinTestFramework(object):
             print("Unexpected exception caught during testing: "+str(e))
             traceback.print_tb(sys.exc_info()[2])
 
+        print("Stopping nodes")
+        stop_nodes(self.nodes)
+        wait_bitcoinds()
+
         if not self.options.nocleanup:
             print("Cleaning up")
-            stop_nodes(self.nodes)
-            wait_bitcoinds()
             shutil.rmtree(self.options.tmpdir)
 
         if success: