Implement cluster connections command

This is the fourth part of cluster show output. We want to push the user to copy some parts of the output of cluster show. If the user wants to connect to the cluster with jdbc they should have the special command to copy. I suggest implementing a cluster connections command that will display connection strings for each connection type. For example:

> cluster connections --jdbc
> jdbc:ignite:thin://1.2.3.4:10300

Now only two connection types are known: jdbc and rest.