This is driven by the fact that OpenSSL 1.1 does not know about SSLv2 at
all and dovecot's defaults simply make OpenSSL error out with "Unknown
protocol 'SSLv2'"[1]. So we change the defaults to refer to SSLv2 iff OpenSSL
seems to know something about it.
While at it, it's also a good idea to disable SSLv3 by default as well.
[1] https://bugs.debian.org/844347
Signed-off-by: Apollon Oikonomopoulos