[tools] Make tools/mb/mb.py work with Python 3

Update the way urllib is imported. As of Python 3, the old `urllib2`
was split into several smaller modules under `urllib`.

This commit unifies the resulting imported names across Python 2 and
Python 3, for forward/backward compatibility.

Bug: v8:9871
Change-Id: I81310ea83536269ae0cdf1406fd69285928c9357
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2848488Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74209}

AUTHORS

@@ -84,6 +84,7 @@ Colin Ihrig <cjihrig@gmail.com>
 Cong Zuo <zckevinzc@gmail.com>
 Daniel Andersson <kodandersson@gmail.com>
 Daniel Bevenius <daniel.bevenius@gmail.com>
+Daniel Dromboski <dandromb@gmail.com>
 Daniel James <dnljms@gmail.com>
 David Carlier <devnexen@gmail.com>
 David Manouchehri <david@davidmanouchehri.com>

tools/mb/mb.py

@@ -27,7 +27,16 @@ import sys
 import subprocess
 import tempfile
 import traceback
-import urllib2
+
+# for py2/py3 compatibility
+try:
+  from urllib.parse import quote
+except ImportError:
+  from urllib2 import quote
+try:
+  from urllib.request import urlopen
+except ImportError:
+  from urllib2 import urlopen
 
 from collections import OrderedDict
 
@@ -1109,7 +1118,7 @@ class MetaBuildWrapper(object):
 
   def CheckCompile(self, builder_group, builder):
     url_template = self.args.url_template + '/{builder}/builds/_all?as_text=1'
-    url = urllib2.quote(
+    url = quote(
             url_template.format(builder_group=builder_group, builder=builder),
             safe=':/()?=')
     try:
@@ -1201,7 +1210,7 @@ class MetaBuildWrapper(object):
 
   def Fetch(self, url):
     # This function largely exists so it can be overridden for testing.
-    f = urllib2.urlopen(url)
+    f = urlopen(url)
     contents = f.read()
     f.close()
     return contents