pack_firmware_functest: Ignore 'INFO:' output

The firmware updater output has been changed in CL:1345611
that verbose messages now goes to stderr with prefix 'INFO:'.

BUG=chromium:
TEST=./pack_firmware_unittest.py; ./pack_firmware_functest.py

Change-Id: I8efb0286613581c045d215b26a6beb26fa52f259
Reviewed-on: https://chromium-review.googlesource.com/1345250
Commit-Ready: Hung-Te Lin <hungte@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Evan Hernandez <evanhernandez@chromium.org>
diff --git a/pack_firmware_functest.py b/pack_firmware_functest.py
index aaa05fe..9506d83 100755
--- a/pack_firmware_functest.py
+++ b/pack_firmware_functest.py
@@ -135,10 +135,11 @@
                                        extra_env={'PATH': new_path},
                                        print_cmd=False)
 
-    # We expect debugging output but should not get anything else.
+    # The stderr may contain debug messages, info, and status (>>).
+    # Anything else (for instance, 'ERROR:') should be error.
     errors = [line for line in result.error.splitlines()
               if line.split() and line.split()[0] not in
-              ['(DEBUG)', 'DEBUG:', '>>']]
+              ['(DEBUG)', 'DEBUG:', '>>', 'INFO:']]
     self.assertEqual(errors, [])
     return result.output.splitlines()