Added ksecprintf for securely printing messages from the kernel.

If SECRET_TESTING is defined, the function will compute and print
a salt value and the hmac/sha256 hash of the message, which can be
verified from the test161 server.

kern/include/kern/secret.h

@@ -45,6 +45,6 @@
  */
 
 #undef SECRET_TESTING
-#define SECRET 0
+#define SECRET ""
 
 #endif /* _SECRET_H_ */

kern/include/test.h

@@ -174,7 +174,9 @@ int ll16test(int, char **);
 #define SUCCESS 0
 #define FAIL 1
 
-void success(bool, uint32_t, const char *);
+int success(bool, const char *, const char *);
+
+int ksecprintf(const char *secret, const char *msg, const char *name);
 
 void random_yielder(uint32_t);
 void random_spinner(uint32_t);