oeqa/commands: Fix compatibility with python 3.9

Python 3.9 dropped isAlive() so use the preferred is_alive().

(From OE-Core rev: 9bb06428cbb2ac0f3d98a1696f050d3393385503)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/commands.py

@@ -125,11 +125,11 @@ class Command(object):
 
     def stop(self):
         for thread in self.threads:
-            if thread.isAlive():
+            if thread.is_alive():
                 self.process.terminate()
             # let's give it more time to terminate gracefully before killing it
             thread.join(5)
-            if thread.isAlive():
+            if thread.is_alive():
                 self.process.kill()
                 thread.join()