Decode key returned from db into unicode.

We get this error in cron:

/usr/local/gerrit/scripts/update_gerrit_users.py:339: UnicodeWarning:
Unicode equal comparison failed to convert both arguments to Unicode -
interpreting them as being unequal
  if key.strip() not in db_keys:

The stuff from Launchpad comes back as unicode, but the stuff from MySQL
comes back as string, which makes the in comparison wonky.

Perhaps we should upgrade the database to unicode properly as well...

Change-Id: I5ef66763429ca490d799ebb5b030abdc4d5de67e
diff --git a/update_gerrit_users.py b/update_gerrit_users.py
index 15baaa9..8fd3a28 100755
--- a/update_gerrit_users.py
+++ b/update_gerrit_users.py
@@ -335,7 +335,7 @@
 
       cur.execute("""select ssh_public_key from account_ssh_keys where
         account_id = %s""", account_id)
-      db_keys = [r[0].strip() for r in cur.fetchall()]
+      db_keys = [r[0].strip().decode('utf-8') for r in cur.fetchall()]
       if key.strip() not in db_keys:
 
         cur.execute("""select max(seq)+1 from account_ssh_keys