cbuildbot_launch: Hide pip install output.

The output of the pip install command contains a warning that has
confused multiple people, so hiding that output. Also add bug number
to log message.

BUG=chromium:764072
TEST=cbuildbot_launch_unittest

Change-Id: I3ac521d38ce4534605f51428b97055f8e3a25c54
Reviewed-on: https://chromium-review.googlesource.com/663759
Tested-by: Don Garrett <dgarrett@chromium.org>
Trybot-Ready: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
diff --git a/scripts/cbuildbot_launch.py b/scripts/cbuildbot_launch.py
index 3c65f84..ff37ea4 100644
--- a/scripts/cbuildbot_launch.py
+++ b/scripts/cbuildbot_launch.py
@@ -268,10 +268,11 @@
   os.environ['LANG'] = 'en_US.UTF-8'
 
   # TODO(dgarrett): Super ugly, super temporary hack to fix release builds.
-  logging.warn('FORCING LOCAL INSTALL OF CRCMOD.')
+  logging.warn('FORCING CRCMOD INSTALL to workaround crbug.com/763438.')
   cmd = ['pip', 'install', '--ignore-installed', 'crcmod']
-  result = cros_build_lib.SudoRunCommand(cmd, error_code_ok=True)
-  logging.warn('FORCED LOCAL INSTALL OF CRCMOD RETURNED: %d', result.returncode)
+  result = cros_build_lib.SudoRunCommand(
+      cmd, error_code_ok=True, mute_output=True)
+  logging.warn('CRCMOD INSTALL RETURNED: %d', result.returncode)
 
 
 def _main(argv):