Update vhost-device-console backend & move it in main workspace

[TimosAmpel]

Summary of the PR

This PR updates the current implementation of vhost-device-console and addresses
the comments noted at the PR #717.

Specifically,

• Eliminates the use of 'select' function and 'nix' dependency
• Registers all input FDs to the main worker epoll handler
• Increases the unit tests' coverage
• Move the device into the main workspace

Requirements

• All commits in this PR have Signed-Off-By trailers (with
  git commit -s), and the commit message has max 60 characters for the
  summary and max 75 characters for each description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• Any newly added unsafe code is properly documented.

[stefano-garzarella]

Summary of the PR

This PR updates the current implementation of vhost-device-console and addresses the comments noted at the PR #717.

Specifically,

* Eliminates the use of 'select' function and 'nix' dependency

Cool, thanks for that!

* Registers all input FDs to the main worker epoll handler

* Increases the unit tests' coverage

* Move the device into the main workspace

All these steps in one commit?

This list should immediately make it clear that we need at least 3/4 separate commits. Please let's try to have commits as small as possible, also to make it easier for reviewers.

[TimosAmpel]

Summary of the PR

This PR updates the current implementation of vhost-device-console and addresses the comments noted at the PR #717.
Specifically,

* Eliminates the use of 'select' function and 'nix' dependency

Cool, thanks for that!

* Registers all input FDs to the main worker epoll handler

* Increases the unit tests' coverage

* Move the device into the main workspace

All these steps in one commit?

This list should immediately make it clear that we need at least 3/4 separate commits. Please let's try to have commits as small as possible, also to make it easier for reviewers.

Thanks for the comment! I did split it into three difference commits, I believe that should be ok.

[stefano-garzarella]

Thanks for the comment! I did split it into three difference commits, I believe that should be ok.

@TimosAmpel thanks for that!

We need to adjust coverage value on both main work space and staging workspace to make CI happy.

Also I suggest better commit title/description, here some suggestions:

• patch 1

vhost-device-console: use worker's epoll for input events

Eliminate the use of select and 'nix' package. This is done by
registering the input events (stdin or tcplistener) onto the main
worker's epoll.

• patch 2

vhost-device-console: improve tests

[add a little descriptions of the new tests]

• patch 3

vhost-device-console: promote to main workspace

The current implementation seems ready to be promoted to the
main workspace since the device supports .... [add what we support, and what is still missing]

[stefano-garzarella]

Are we supporting these?