BUG/MINOR: server: fix check reuse-pool in srv_settings_cpy()

<reuse_pool> may be set on check to instruct that connection reuse may
be performed for server health checks.

As expected, this field is duplicated in srv_settings_cpy(). However,
there is an exception for rHTTP servers as in this case check-reuse-pool
must be forcefully activated, as performed in srv_settings_init(). Thus,
the value was not copied to avoid changing it to 0.

This causes a configuration issue with rHTTP on server-template though.
In this case, check-reuse-pool is not set for duplicated server
instances as srv_settings_init() is not called for them. This causes
checks to always fail for such entries.

Fix this by forcing check-reuse-pool for rHTTP in srv_settings_cpy(),
and duplicate the values for other servers.

This must be backported up to 3.2.