Comment 3 for bug 1260193

Since gu::Config::parse itself doesn't know about parameters to
distinguish between in/valid parameters, right step here would
be to initialise map with compile-time values (as is done in
galera::ReplicatorSMM::ReplicatorSMM for others), and not to add any
new keys in gu::Config::parse but to throw exception when there is a
new key. , ie. move gu::Config::parse to a latter stage after initialisation of config_ map with compile time values.