MINOR: SSL: add client/server random sample fetches

MINOR: SSL: add client/server random sample fetches

This adds 4 sample fetches:
- ssl_fc_client_random
- ssl_fc_server_random
- ssl_bc_client_random
- ssl_bc_server_random

These fetches retrieve the client or server random value sent during the
handshake.

Their use is to be able to decrypt traffic sent using ephemeral ciphers. Tools
like wireshark expect a TLS log file with lines in a few known formats
(https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=epan/dissectors/packet-tls-utils.c;h=28a51fb1fb029eae5cea52d37ff5b67d9b11950f;hb=HEAD#l5209).
Previously the only format supported using data retrievable from HAProxy state
was the one utilizing the Session-ID. However an SSL/TLS session ID is
optional, and thus cannot be relied upon for this purpose.

This change introduces the ability to extract the client random instead which
can be used for one of the other formats. The change also adds the ability to
extract the server random, just in case it might have some other use, as the
code change to support this was trivial.