REORG: init: encapsulate code that reads cfg files

REORG: init: encapsulate code that reads cfg files

Haproxy master process should not read its configuration the second time
after performing reexec and passing to MODE_MWORKER_WAIT. So, to make
this part of init() function more readable and to distinguish better the
point, where configs have been read, let's encapsulate it in a separate
function.