autotest_quickmerge: fix output encoding

We parse the rsync output as text, so set the encoding to utf-8.

BUG=chromium:1055903
TEST=CQ passes

Change-Id: I91bf6abc0896cec0850c9fa8154162538f827ab2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2072702
Reviewed-by: Juston Li <juston.li@intel.corp-partner.google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Juston Li <juston.li@intel.corp-partner.google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/autotest_quickmerge.py b/scripts/autotest_quickmerge.py
index ef9d0a3..29621c1 100644
--- a/scripts/autotest_quickmerge.py
+++ b/scripts/autotest_quickmerge.py
@@ -295,7 +295,7 @@
 
   command += [source_path, sysroot_autotest_path]
 
-  return cros_build_lib.sudo_run(command, stdout=True)
+  return cros_build_lib.sudo_run(command, stdout=True, encoding='utf-8')
 
 
 def ParseArguments(argv):