kdc: refactor Samba-specific auditing API in terms of existing API

Make Samba-specific HDB auth status API a wrapper on the existing auditing API,
with a view towards unifying the two APIs in a future commit.

The term "auth status" is replaced with "auth event", and the HDB auth_status
method is replaced with a more general purpose audit method which has access to
the entire request structure.

lib/base/heimbase-svc.h

@@ -70,7 +70,8 @@
     const char *e_text;                                         \
     char *e_text_buf;                                           \
     heim_string_t reason;                                       \
-    heim_array_t kv;                                            \
+    /* auditing key/value store */                              \
+    heim_dict_t kv;                                             \
     int32_t ret
 
 #endif /* HEIMBASE_SVC_H */