Fix presubmit errors in update_flaky_expectations.py by styling const.

Fixes pylint presubmit errors in the update_flaky_expectations.py
script by adhering to constant styling.

Bug: 730704
Change-Id: I365f2f642b1e64c6b1ee1837be99819a95b1e160
Reviewed-on: https://chromium-review.googlesource.com/1067521Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Commit-Queue: Bugs Nash <bugsnash@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560853}

third_party/blink/tools/update_flaky_expectations.py

@@ -12,7 +12,7 @@ from blinkpy.web_tests.layout_package.bot_test_expectations import BotTestExpect
 
 
 if __name__ == "__main__":
-    host = host.Host()
-    return_code = update_flaky_expectations.main(
-        host, BotTestExpectationsFactory(host.builders), sys.argv[1:])
-    sys.exit(return_code)
+    HOST = host.Host()
+    RETURN_CODE = update_flaky_expectations.main(
+        HOST, BotTestExpectationsFactory(HOST.builders), sys.argv[1:])
+    sys.exit(RETURN_CODE)