There must be summary functionality for hosts

[terciodemelo]

Given a list of Hosts we should be able to summarize the following information:

• Host ID
• How many users are in the host
• List all users in the host
  • If the user is sudoer or not
  • If the user is password authenticable
  • If the user is authenticable through identity file
    • If so, how many public key does this user have
  • When the user was added

Besides, there are requirements for this functionality:

• Preferably there should be no extra files in the host, if it can be avoided
• The host must have an unique ID so that even if it's past IP/domain was taken by other Host, the second host should not be mistaken for the first
• If the host is not accessible (not reachable, failed authentication, etc) a clear response should be given so that the issue can be easily understood by the user. Given the nature of this project it is utterly unacceptable to make the user uncertain, feeling unsafe, or lost. Security and transparency are our top priorities