BUG/MINOR: check: fix leak on add dynamic server with agent-check error

BUG/MINOR: check: fix leak on add dynamic server with agent-check error

If an error occured during a dynamic server creation, free_check is used
to liberate a possible agent-check. However, this does not free
associated vars and rules associated as this is done on another function
named deinit_srv_agent_check.

To simplify the check free and avoid a leak, move free vars/rules in
free_check. This is valid because deinit_srv_agent_check also uses
free_check.

This operation is done only for an agent-check because for a health
check, the proxy instance is the owner of check vars/rules.

This should not be backported, unless dynamic server checks are
backported.