Add -client_renegotiation flag support.  The -client_renegotiation flag is
equivalent to SSL_OP_ALLOW_CLIENT_RENEGOTIATION. Add support to the app,
the config code, and the documentation.

Add SSL_OP_ALLOW_CLIENT_RENEGOTIATION to the SSL tests. We don't need to
always enable it, but there are so many tests so this is the easiest thing
to do.

Add a test where client tries to renegotiate and it fails as expected. Add
a test where server tries to renegotiate and it succeeds. The second test
is supported by a new flag, -immediate_renegotiation, which is ignored on
the client.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NTomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15184)