Add terminal-only appvms

[msm-code]

• I tested it locally.
• I tried to run at least one application VM and it works.

Add terminal-only appvms

I hope this change is not too controversial.

Sometimes I want to run a VM without a window running in the foreground.
For example, a router/firewall VM, temporary VM for compiling some untrusted
code or installing a random package from the internet. Full GUI is usually
unnecessary, since it's much nicer to be able to use host's terminal directly.

In this change I add --cli switch that disables GUI window.

Initially I also added serial device to domain (this allowed automatic connect
with virsh -c qemu:///system console appvm_name), but I dropped it before
making a PR - adding a SSH server to appvm definition works better for me.

I also change networking model from qemu to virtmanager's device (virbr0).
The reason for this is that it's much easier for me to configure firewall/
iptables with virt manager network, than with qemu device. Also AppVMs
don't have IPs with qemu device, I think. If this change is not OK I'm
happy to keep this change only in my fork (or maybe as a switch
--networking-model?)

Thoughts?

[jollheef]

Hello,

Thanks for the pull request.

All those changes are fit the initial idea, so does not looks controversial for me.

Regarding the networking model, I think introducing switch --networking-model is the best way to make it right.

In general, looks good to me. However, aside from introducing switch, please make each feature in separate commits and rewrite the commit message (too much unnecessary info).

[msm-code]

Sure, making two separate changes makes a lot of sense.

Regarding the networking model, I think introducing switch --networking-model is the best way to make it right.

It doesn't make sense to have both --offline and --networking-model so maybe they should be merged? What do you think about it taking a role of a current --offline switch? So you'd have:

--networking=qemu
--networking=libvirt
--networking=offline  # or =none?

Otherwise I can just throw an error where both are specified.

[jollheef]

I don't think it's a problem to have some duplicity. Also for some people (like me also) type --offline just more convenient.

So it's better to throw an error if someone has specified --networking=!offline and at the same time used --offline.

[msm-code]

I agree that --offline is more convenient than long --networking=offline. I'll add this networking changes in a separate PR then.