MEDIUM: ssl/cli: 'set ssl cert' updates a certificate from the CLI

MEDIUM: ssl/cli: 'set ssl cert' updates a certificate from the CLI

    $ echo -e "set ssl cert certificate.pem <<\n$(cat certificate2.pem)\n" | \
    socat stdio /var/run/haproxy.stat
    Certificate updated!

The operation is locked at the ckch level with a HA_SPINLOCK_T which
prevents the ckch architecture (ckch_store, ckch_inst..) to be modified
at the same time. So you can't do a certificate update at the same time
from multiple CLI connections.

SNI trees are also locked with a HA_RWLOCK_T so reading operations are
locked only during a certificate update.

Bundles are supported but you need to update each file (.rsa|ecdsa|.dsa)
independently. If a file is used in the configuration as a bundle AND
as a unique certificate, both will be updated.

Bundles, directories and crt-list are supported, however filters in
crt-list are currently unsupported.

The code tries to allocate every SNIs and certificate instances first,
so it can rollback the operation if that was unsuccessful.

If you have too much instances of the certificate (at least 20000 in my
tests on my laptop), the function can take too much time and be killed
by the watchdog. This will be fixed later. Also with too much
certificates it's possible that socat exits before the end of the
generation without displaying a message, consider changing the socat
timeout in this case (-t2 for example).

The size of the certificate is currently limited by the maximum size of
a payload, that must fit in a buffer.