h_GetHost_r cleanup cases

h_GetHost_r cleanup cases

avoid potentially leaking a cb_in or a capabilities blob;
use a common exit function and free when these were left set.

Reviewed-on: http://gerrit.openafs.org/496
Tested-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>