findmissing: Explicitly import MySQLdb.constants.ER

On GCE, MySQLdb.constants.ER is only available if it is imported
explicitly.

BUG=None
TEST=Run on GCE

Change-Id: I763c9c1cb7a50950b3b09d894ebc2d1bb108fdd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2197577
Reviewed-by: Curtis Malainey <cujomalainey@chromium.org>
Commit-Queue: Guenter Roeck <groeck@chromium.org>
Tested-by: Guenter Roeck <groeck@chromium.org>
diff --git a/contrib/findmissing/initdb_upstream.py b/contrib/findmissing/initdb_upstream.py
index 453fae3..d86c5a7 100755
--- a/contrib/findmissing/initdb_upstream.py
+++ b/contrib/findmissing/initdb_upstream.py
@@ -12,6 +12,7 @@
 import re
 import subprocess
 import MySQLdb
+import MySQLdb.constants.ER
 import common