implementation of WFLY-2510

Add CLI command to display information about current connection.
Should it print username = $local ?
I thought about using a description because the "$local" is not intuitive about the current user. 

:whoami
{
    "outcome" => "success",
    "result" => {"identity" => {
        "username" => "$local",
        "realm" => "ManagementRealm"
    }}
}