Make build reproducible

Currently in master, cloudkitty is leaking the build hostname in the
cloudkitty.conf file when generating it. This makes the entire package
no reproducible.

This patch adds a sample_default= argument when defining host=, so that
the default value when generating the config file is *not* the hostname
of the build host. This doesn't change at all the behavior, which will
use the hostname FQDN if the value isn't set by the user.

Change-Id: I59eb50018dd895f40ff949123c4ab78360c74850

cloudkitty/service.py

@@ -30,6 +30,7 @@ from cloudkitty import version
 service_opts = [
     cfg.StrOpt('host',
                default=socket.getfqdn(),
+               sample_default='<server-hostname.example.com>',
                help='Name of this node. This can be an opaque identifier. '
                'It is not necessarily a hostname, FQDN, or IP address. '
                'However, the node name must be valid within an AMQP key, '