Driver that uses rpiboot to boot a raspberry pi as a mass storage device

[benjamin1313]

This adds a driver and resource that can be used to take a raspberry pi put into usbboot mode and boot it as a mass storage device.
This is helpful when working with hardware based around raspberry pi compute modules, which might use a ssd or emmc for storage instead of a sd-card.

Currently being use to bootstrap a 10' chipsee panel before running automated tests.
The script used for this has been added to examples.

For this implementation it was chosen to keep it simple and not add support for using a serial number to chose between multiple devices because when adding the -i argument to the rpiboot like so rpiboot -i [serialno] i experienced that rpiboot would sit and wait for a raspberry pi to connect instead of using the one already connected. Which then leave me in a situation where labgrid is stuck executing the rpiboot command, waiting for the pi to be rebooted but not being able to do so because labgrid is stuck in the rpiboot command.

Checklist

• Documentation for the feature

• The arguments and description in doc/configuration.rst have been updated

• PR has been tested

[codecov]

Codecov Report

❌ Patch coverage is 52.83019% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.4%. Comparing base (e9e43aa) to head (1ac9a8c).
⚠️ Report is 151 commits behind head on master.

Files with missing lines	Patch %	Lines
labgrid/driver/rpibootdriver.py	66.6%	8 Missing ⚠️
labgrid/resource/udev.py	42.8%	8 Missing ⚠️
labgrid/remote/exporter.py	0.0%	7 Missing ⚠️
labgrid/resource/remote.py	71.4%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1734   +/-   ##
======================================
  Coverage    45.4%   45.4%           
======================================
  Files         172     173    +1     
  Lines       13500   13553   +53     
======================================
+ Hits         6130    6158   +28     
- Misses       7370    7395   +25     

Flag	Coverage Δ
3.10	45.4% <52.8%> (+<0.1%)	⬆️
3.11	45.4% <52.8%> (+<0.1%)	⬆️
3.12	45.4% <52.8%> (+<0.1%)	⬆️
3.13	45.4% <52.8%> (+<0.1%)	⬆️
3.9	45.4% <52.8%> (+<0.1%)	⬆️

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