depot_tools: Run some tests on Python 3 on the bots.

Bug: 984182
Change-Id: I0b7f1e3e056548a27a416c9b4078e54c9e5d60d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1769400
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@google.com>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
diff --git a/gclient_utils.py b/gclient_utils.py
index 45617df..7b4ae56 100644
--- a/gclient_utils.py
+++ b/gclient_utils.py
@@ -916,7 +916,7 @@
     running = self.running
     self.running = []
     for t in running:
-      if t.isAlive():
+      if t.is_alive():
         self.running.append(t)
       else:
         t.join()