Reland "Print ps in intervals while the process is running"

This is a reland of 50c6d8d348

Original change's description:
> Print ps in intervals while the process is running
>
> R=apolito@google.com, ehmaldonado@chromium.org
>
> Bug: 1074355
> Change-Id: Id2d5c8ca6f27fefb0fe8d769ae2e50dbaaddadbb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2167221
> Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
> Reviewed-by: Anthony Polito <apolito@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

R=apolito@google.com, ehmaldonado@chromium.org

Bug: 1074355
Change-Id: I488b521e4a3b859c37f0bb1e21cad7d037f8f97e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2169392
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

recipes/recipe_modules/bot_update/resources/bot_update.py

@@ -117,11 +117,16 @@ class PsPrinter(object):
     self.active = sys.platform.startswith('linux2')
     self.thread = None
 
-  @staticmethod
-  def print_pstree():
+  def print_pstree(self):
     """Debugging function used to print "ps auxwwf" for stuck processes."""
+    # Add new line for cleaner output
+    print()
     subprocess.call(['ps', 'auxwwf'])
 
+    # Restart timer, we want to continue printing until the process is
+    # terminated.
+    self.poke()
+
   def poke(self):
     if self.active:
       self.cancel()