Fixed logging messages for transport security options (#2310)

[0x7162]

Old behavior:

>>> import paramiko
>>> import socket
>>> s = socket.socket()
>>> t = paramiko.Transport(s)
>>> opts = t.get_security_options()
>>> for prop in ('ciphers', 'digests', 'key_types', 'kex'):
...   try:
...     setattr(opts, prop, ['unknown'])
...   except ValueError as e:
...     print('%s: %r' % (prop, e))
...
ciphers: ValueError('unknown cipher')
digests: ValueError('unknown cipher')
key_types: ValueError('unknown cipher')
kex: ValueError('unknown cipher')

New behavior:

import paramiko
import socket
s = socket.socket()
t = paramiko.Transport(s)
opts = t.get_security_options()

for prop in ('ciphers', 'digests', 'key_types', 'kex'):
    try:
        setattr(opts, prop, ['unknown'])
    except ValueError as e:
        print(e)

unknown ciphers name: ('unknown',), possible options: ['aes128-ctr', 'aes192-ctr', 'aes256-ctr', 'aes128-cbc', 'aes192-cbc', 'aes256-cbc', '3des-cbc']

unknown macs name: ('unknown',), possible options: ['hmac-sha1', 'hmac-sha1-96', 'hmac-sha2-256', 'hmac-sha2-256-etm@openssh.com', 'hmac-sha2-512', 'hmac-sha2-512-etm@openssh.com', 'hmac-md5', 'hmac-md5-96']

unknown keys name: ('unknown',), possible options: ['ssh-rsa', 'ssh-rsa-cert-v01@openssh.com', 'rsa-sha2-256', 'rsa-sha2-256-cert-v01@openssh.com', 'rsa-sha2-512', 'rsa-sha2-512-cert-v01@openssh.com', 'ssh-dss', 'ssh-dss-cert-v01@openssh.com', 'ecdsa-sha2-nistp256', 'ecdsa-sha2-nistp256-cert-v01@openssh.com', 'ecdsa-sha2-nistp384', 'ecdsa-sha2-nistp384-cert-v01@openssh.com', 'ecdsa-sha2-nistp521', 'ecdsa-sha2-nistp521-cert-v01@openssh.com', 'ssh-ed25519', 'ssh-ed25519-cert-v01@openssh.com']

unknown kex name: ('unknown',), possible options: ['diffie-hellman-group1-sha1', 'diffie-hellman-group14-sha1', 'diffie-hellman-group-exchange-sha1', 'diffie-hellman-group-exchange-sha256', 'diffie-hellman-group14-sha256', 'diffie-hellman-group16-sha512', 'gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==', 'gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==', 'gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==', 'ecdh-sha2-nistp256', 'ecdh-sha2-nistp384', 'ecdh-sha2-nistp521', 'curve25519-sha256@libssh.org']

[0x7162]

Sorry for tagging you @bskinn,
but it looks like you triaged and labeled other PRs here.

I think this PR is ready to go - what is the process to settle it down?
I didn't find the process flow description neither in repo nor in the official doc ( https://www.paramiko.org/contributing.html )

[bskinn]

No worries, @0x7162 -- yeah, I'm working my way through the notifications backlog, piecewise.

The substance looks good to me, to flag for bitprophet's review. (I'm only triaging, I'm not a maintainer.) The only thing I see is to add a CHANGELOG snip, at /sites/www/changelog.rst.

Other than that, there isn't really a process, just waiting for bitprophet's review and eval. Unfortunately, I know he's in the midst of a dry spell at the moment in terms of his open source bandwidth, so I can't give a timeline on when review will happen.

Really appreciate the contribution!

[0x7162]

@bskinn I added the changelog, please verify it is a correct change