Rex::Socket::SslTcp set cipher and verify_mode

Update Rex::Socket::SslTcp to accept verification mode string from
Rex::Socket::Parameters, which has been modified accordingly.
Add SSLVerifyMode and SSLCipher options (params and socket work
were done before, but the option was not exposed) to
Msf::Exploit::Tcp.

Testing:
```
>> sock = Rex::Socket::Tcp.create('PeerHost'=>'10.1.1.1','PeerPort'
=>443,'SSL' => true, 'SSLVerifyMode' => 'NONE')
>> sock.sslctx.verify_mode
=> 0
>> sock.close
=> nil
>> sock = Rex::Socket::Tcp.create('PeerHost'=>'10.1.1.1','PeerPort'
=>443,'SSL' => true, 'SSLVerifyMode' => 'PEER')
=> #<Socket:fd 13>
>> sock.sslctx.verify_mode
=> 1
```

Note: this should be able to resolve the recent SSL socket hackery
of exploit/linux/misc/nagios_nrpe_arguments.