fix: sim_vehicle.py's under_vagrant util doesn't appropriately check whether the script is run in a Vagrant VM

[JohannPally]

Within the spun up Vagrant VM, in a Python REPL, the current implementation evals to False

vagrant@ubuntu-jammy:~$ python
Python 3.10.12 (main, Aug 15 2025, 14:32:43) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> print(os.path.isfile("/ardupilot.vagrant"))
False

... with the suggested change

>>> os.path.isdir("/vagrant")
True

[peterbarker]

So the Vagrant install scripts are supposed to create the missing file.

Something is obviously not working there!

https://github.com/ardupilot/ardupilot/blob/master/Tools/vagrant/initvagrant.sh#L102
https://github.com/ardupilot/ardupilot/blob/master/Tools/vagrant/initvagrant-trusty64.sh#L42

... that being said, I think the reasons for needing that separate file are history now (IIRC it wasn't always /vagrant as a mountpoint!)

... so I'm inclined to merge this once it passes CI.

You need to fix the commit message, something like "Tools: sim_vehicle.py: look for /vagrant when determining if we are running under Vagrant".

A couple of extra suitably-named commits for removing the lines I referenced above would be a bonus :-)

[peterbarker]

I've fixed the commit message and marked for merge.

Note I was refering to the commit message, not the title of the PR in github

Thanks!