didn't work as expected: collation_server was set not to xxx,
but to the default collation of character set "yyy".
    
With different argument order it worked as expected:
mysqld --character-set-server=yyy --collation-server=yyy 
    
Fix:
initializate default_collation_name to 0
when processing --character-set-server
only if --collation-server has not been specified
in command line.