Use SQLite3 based authentication

The user data is now stored inside a SQLite3 database. By storing the data
inside a database, we remove the restriction that the previous hashtable
based implementation had.

server/modules/authenticator/GSSAPI/GSSAPIAuth/gssapi_auth.c

@@ -20,11 +20,9 @@
 #include <maxscale/protocol/mysql.h>
 #include <maxscale/secrets.h>
 #include <maxscale/mysql_utils.h>
+#include <maxscale/sqlite3.h>
 #include "../gssapi_auth.h"
 
-/** Default timeout is one minute */
-#define MXS_SQLITE_BUSY_TIMEOUT 60000
-
 /**
  * MySQL queries for retrieving the list of users
  */