token_restriction: Add non-token merge exception
token_restriction: Add non-token merge exception

Add exception that is thrown when merging of token and non-token 
restrictions is attempted. Before this change only merging non-token
and token restriction was validated (WHERE pk = 0 AND token(pk) > 0)
and not the other way (WHERE token(pk) > 0 AND pk = 0).

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla