Adding ability to authenticate jump host using certificate and some other helpful functions

[jeremygiberson-at-privoro]

This PR is not intended to be merged, I just wanted to show the changes I've made for our use case and get some feedback on whether some of these changes would be welcome into the main project.

Use Case

In my use case I'm spawning kafka-tunnel from a script (node, but that's not really important) to setup kafka access so I can perform data collection and exit. Ideally, this is an all in one script. So I don't run kafka-tunnel separately, then run my script, the script runs kafka-tunnel itself.

non-graceful exit cleanup

The first changes I added was a command to delete interfaces (cleanmanual and cleanaws). This was because when I terminated my script (and it terminated kafka-tunnel) the interfaces were left registered. So I added these two commands as mirrors to aws and manual so you can remove the interfaces if they don't get cleaned up.

But additionally, in order to eliminate the need of having to clean them up, I added signal handlers for SIGINT and SIGQUIT to clean them up when those signals are received. But I suspect there are a few other edge cases where kafka-tunnel could exit without cleaning up.
Would you be interested in the signal handler catching & cleanup PR?
Would you be interested in manualclean and awsclean command PR?

Jump Host Authentication via Certificate

We use public/private keys to ssh into our jump host. So I needed a way to provide the path to the private key to the SSH call. I added the options -jc --jump_host_cert to provide this path.
Would you be interested in a jump host cert PR?

SSH No commands option

Because we're running kafka-tunnel from a script, a tty-terminal is not available to ssh. I'm passing -N option to ssh to get around this. This eliminates the open terminal to the jump host. I wasn't sure what I wanted to do to make this configurable. The easy answer is add a new option ie -nc --no_commands, but I'm wondering if there is a better convention to support passing through 1 or more options to SSH, than exposing all the potentially ssh options a user might want to the kafka-tunnel command options. Is there a method to provide a repeatable option that gets passed through? Ie -S "-i /path/to/key" -S "-N"?
Would you be interested in a custom/extra SSH options PR?
Do you have recommendations on how to provide the custom options beside mirroring the options in the aws and manual commands?

I'd be happy to make separate PR's for each feature you're interested in.

Thanks