Add timeout argument to ssh_connect() nasl function

[jjnicola]

What:
Add timeout argument to ssh_connect() nasl function to set the connection timeout in seconds

Why:
Some ssh server take too long to return the prompt for the password

How:
As I didn't have a ssh server with the issue, I have used the paramiko server demo and added some sleep() before returning the prompt. That simulates the issue in the server side. Then, I used the next nasl script:

openvas-nasl -X -B -d -i /home/jnicola/install/var/lib/openvas/plugins -t localhost ssh_timeout.nasl

login = "robey";
password = "foo";
port = 2200;

#Sockets
  soc = open_sock_tcp( port );
  if( ! soc ) exit( 0 );
  display ("socket opened:",soc);

#Use the new timeout option. It must be greather than the sleep set in the demo server
  sess = ssh_connect( socket:soc, timeout:15 );
  display("session: ", sess);

if( ! sess )
  return 0;

if( ssh_userauth( sess, login:login, password:password ) ) {
  ssh_disconnect( sess );
  last_sess = 0;
  return 0;
}

Checklist:

• Tests
• CHANGELOG Entry

[cfi-gb]

Approving the text / description changes.