Check that we can verify a signature at initialisation time

Check that we can verify a signature at initialisation time

Fedora 33 doesn't support RSASHA1 in future mode.  There is no easy
check for this other than by attempting to perform a verification
using known good signatures.  We don't attempt to sign with RSASHA1
as that would not work in FIPS mode.  RSASHA1 is verify only.

The test vectors were generated using OpenSSL 3.0 and
util/gen-rsa-sha-vectors.c.  Rerunning will generate a new set of
test vectors as the private key is not preserved.

e.g.
	cc util/gen-rsa-sha-vectors.c -I /opt/local/include \
		-L /opt/local/lib -lcrypto