making test configs closer to default config

This swaps out localhost for 127.0.0.1 in ipv6.cfg.
The ambition here is to have it more akin to the default
configs. localhost worked, but I like 127.0.0.1 better
(since ::1 is needed anyways).

tests/configs/ipv6.cfg

@@ -7,7 +7,7 @@ pid_file=run/nrpe.pid
 server_port=40321
 #server_address=127.0.0.1
 #server_address=0.0.0.0,::
-allowed_hosts=localhost,::1
+allowed_hosts=127.0.0.1,::1
 
 dont_blame_nrpe=0
 allow_bash_command_substitution=0