Add QEMUDriver.interact() and qemu-run.py example

[Bastian-Krause]

Description
Since the QEMUDriver can't be used with labgrid-client (because it does not use labgrid's remote infrastructue), there is currently no good way of accessing its console interactively, e.g. for debugging.

Add a QEMUDriver.interact() method that creates a PTY, let microcom open it and relay the QEMUDriver's input and output to that PTY.

Add an example helper to run QEMU, either by activating the QEMUDriver directly or by transitioning into a strategy state first, then start an interactive console.

Checklist

• PR has been tested

[codecov]

Codecov Report

❌ Patch coverage is 16.00000% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.9%. Comparing base (3466688) to head (11e0ffb).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
labgrid/driver/qemudriver.py	16.0%	21 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1892     +/-   ##
========================================
- Coverage    46.0%   45.9%   -0.1%     
========================================
  Files         180     180             
  Lines       14471   14496     +25     
========================================
+ Hits         6662    6666      +4     
- Misses       7809    7830     +21     

Flag	Coverage Δ
3.10	45.9% <16.0%> (-0.1%)	⬇️
3.11	45.9% <16.0%> (-0.1%)	⬇️
3.12	45.9% <16.0%> (-0.1%)	⬇️
3.13	45.9% <16.0%> (-0.1%)	⬇️
3.14	45.9% <16.0%> (-0.1%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

[a3f]

I just gave it a try and wondering if there is a good way to terminate microcom when qemu exits?
Also, it's not possible to just spawn qemu with this, unless pytest has been called with -s in the first place. Could that be solved somehow? FWIW, here is what I did before:

cmd = self.qemu.get_qemu_base_args()

with open("/dev/tty", "r+b", buffering=0) as tty:
    tty.write(bytes("Run manually with: \n{} -serial mon:stdio\n".format(quote_cmd(cmd)), "UTF-8"))
    if state == "qemu_dry_run":
        pytest.exit('Dry run. Terminating.')
    subprocess.run(cmd, stdin=tty, stdout=tty, stderr=tty)