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.
and userspace.
In userspace, this is accessed through #include <secure.h>
In the kernel, this is access through #include <kern/secure.h>
There is a unit test for this (hm1) that computes the hmac and compares it to
the known value. The salted vesion tested offline.
-----
Also, fixed usespace compile issue with not changing KERNEL_SECRET => SECRET.
