For various reasons, this was a nontrivial movement. There are
several places in the code where we do something like "update the
flags on this routerstatus or node if we're an authority", and at
least one where we pretended to be an authority when we weren't.
signed_descriptor_digest has a length of DIGEST_LEN but the memset
used to fill it used DIGEST256_LEN.
Signed-off-by: Kris Katterjohn <katterjohn@gmail.com>
Additionally, use it to test that is_staledesc is set correctly.
Eventually we'll want to test all the other flags, but I'm aiming
for only adding coverage on the changed code here.
