MINOR: server: Extract the code responsible of copying default-server settings.

MINOR: server: Extract the code responsible of copying default-server settings.

This patch moves the code responsible of copying default server settings
to a new server instance from parse_server() function to new defsrv_*_cpy()
functions which may be used both during server lines parsing and during server
templates initializations to come.

These defsrv_*_cpy() do not make any reference to anything else than default
server settings.