Use urllib2 in roll_deps, which raises on non-200 HTTP status

This ensures that on service outages we get a clear early error message instead of something cryptic later down the line

Bug: None
Change-Id: Ib637ed97144284e3744aaa948f594f5795fa9c72
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/18040
Reviewed-by: Edward Lemur <ehmaldonado@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20545}

tools_webrtc/autoroller/roll_deps.py

@@ -17,7 +17,7 @@ import os
 import re
 import subprocess
 import sys
-import urllib
+import urllib2
 
 
 # Skip these dependencies (list without solution name prefix).
@@ -170,7 +170,7 @@ def ReadRemoteCrCommit(revision):
 
 def ReadUrlContent(url):
   """Connect to a remote host and read the contents. Returns a list of lines."""
-  conn = urllib.urlopen(url)
+  conn = urllib2.urlopen(url)
   try:
     return conn.readlines()
   except IOError as e: