stream-ssl: Get peer-ca-cert functionality to work.

stream-ssl: Get peer-ca-cert functionality to work.

When --certificate option is provided, we currently use
SSL_CTX_use_certificate_chain_file() function to add
that certificate. If our single certificate file had multiple
certificates (as a chain), all of them would get added and sent
to the remote peer. But once you call
SSL_CTX_use_certificate_chain_file(), any future calls to
SSL_CTX_add_extra_chain_cert() (called when --peer-ca-cert option
is used) had no effect.

Since our man pages and INSTALL.SSL.md say that --certificate
is used to specify one certificate and additional certificates
are sent via --peer-ca-cert, this commit changes
SSL_CTX_use_certificate_chain_file() use to
SSL_CTX_use_certificate_file(). With this, additional certificates
can now be added via --peer-ca-cert option.

The test case added with this commit would fail without the
above changes.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>