Replace apps/server.pem with certificate with a sha256 signature.

Replace apps/server.pem with certificate with a sha256 signature.

It replaces apps/server.pem that used a sha1 signature with a copy of
test/certs/servercert.pem that is uses sha256.

This caused the dtlstest to start failing. It's testing connection
sbetween a dtls client and server. In particular it was checking that if
we drop a record that the handshake recovers and still completes
successfully. The test iterates a number of times. The first time
through it drops the first record. The second time it drops the second
one, and so on. In order to do this it has a hard-coded value for the
expected number of records it should see in a handshake. That's ok
because we completely control both sides of the handshake and know what
records we expect to see. Small changes in message size would be
tolerated because that is unlikely to have an impact on the number of
records. Larger changes in message size however could increase or
decrease the number of records and hence cause the test to fail.

This particular test uses a mem bio which doesn't have all the CTRLs
that the dgram BIO has. When we are using a dgram BIO we query that BIO
to determine the MTU size. The smaller the MTU the more fragmented
handshakes become. Since the mem BIO doesn't report an MTU we use a
rather small default value and get quite a lot of records in our
handshake. This has the tendency to increase the likelihood of the
number of records changing in the test if the message size changes.

It so happens that the new server certificate is smaller than the old
one. AFAICT this is probably because the DNs for the Subject and Issuer
are significantly shorter than previously. The result is that the number
of records used to transmit the Certificate message is one less than it
was before. This actually has a knock on impact for subsequent messages
and how we fragment them resulting in one less ServerKeyExchange record
too (the actual size of the ServerKeyExchange message hasn't changed,
but where in that message it gets fragmented has). In total the number
of records used in the handshake has decreased by 2 with the new
server.pem file.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
GH: #10784