parallel_emerge: implement rich comparison methods

Python 3 dropped support for __cmp__ so classes have to implement the
full suite of comparison methods now.  Since score is a tuple of ints,
we can test them directly.

BUG=chromium:980619
TEST=unittests pass before & after change

Change-Id: I706ed9f06887693424d5b63e12567ec9cafa6ac1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1688538
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/parallel_emerge.py b/scripts/parallel_emerge.py
index 62b4bf9..b3c69b9 100644
--- a/scripts/parallel_emerge.py
+++ b/scripts/parallel_emerge.py
@@ -1278,8 +1278,23 @@
     self.score = None
     self.update_score()
 
-  def __cmp__(self, other):
-    return cmp(self.score, other.score)
+  def __lt__(self, other):
+    return self.score < other.score
+
+  def __le__(self, other):
+    return self.score <= other.score
+
+  def __eq__(self, other):
+    return self.score == other.score
+
+  def __ne__(self, other):
+    return self.score != other.score
+
+  def __gt__(self, other):
+    return self.score > other.score
+
+  def __ge__(self, other):
+    return self.score >= other.score
 
   def update_score(self):
     self.score = (