MINOR: server: ensure check-reuse-pool is init in srv_settings_init()

MINOR: server: ensure check-reuse-pool is init in srv_settings_init()

For rHTTP servers, check-reuse-pool is forcefully set on them, else
checks would always fail. This initialization was performed in
_srv_parse_init().

Move this force init in srv_settings_init(). This is a better place as
_srv_parse_init() should only perform minimal configuration, mostly
related to server address. Then srv_settings_init() is called with the
task to set every fields to suitable default values before keywords
parsing.

Also, this ensures that check-reuse-pool is set to 0 for non rHTTP
servers. This is not strictly required though as server structure is
calloc'ed.