MXS-1220: Add HTTP BA authentication

The admin interface now supports Basic Access authentication. This is not
a secure method of authentication and it should not be used without
unencrypted connections.

Made the admin interface port, authentication, username and password
configurable.

include/maxscale/adminusers.h.in

@@ -30,6 +30,9 @@ MXS_BEGIN_DECLS
 /** Default user for the administrative interface */
 #define DEFAULT_ADMIN_USER "@DEFAULT_ADMIN_USER@"
 
+static const char INET_DEFAULT_USERNAME[] = "admin";
+static const char INET_DEFAULT_PASSWORD[] = "mariadb";
+
 /*
  * MySQL session specific data
  *