Tests: USB: Use libusb0 backend on Windows

[fkjagodzinski]

Description

libusb0 supports all features used for testing. A newer version (libusb1) does not have a complete implementation for Windows.

Moreover, this will stop our USB device tests from using a libusb-1.0.dll which may have been copied to the Python directory by the user (i.e. following pyOCD installation procedure).

Pull request type

[ ] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[x] Test update
[ ] Breaking change

Reviewers

@jeromecoutant, @jamesbeyond

Release Notes

[ciarmcom]

@fkjagodzinski, thank you for your changes.
@jamesbeyond @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

@jamesbeyond Please review

[jeromecoutant]

Hi
I am currently trying to debug with the USB serial test...
And maybe current patch is not complete...

I could start pyocd gdbserver,
but test couldn't be run:

[1569231275.73][HTST][ERR] host test not detected: usb_device_serial

[fkjagodzinski]

[1569231275.73][HTST][ERR] host test not detected: usb_device_serial

@jeromecoutant If you use htrun you should add a -e flag to specify host test directory, e.g. mbedhtrun --skip-flashing --skip-reset -p COM31:9600 -e "TESTS\host_tests".

[maciejbocianski]

LGTM

[jamesbeyond]

hey @fkjagodzinski, what is the impact to the test setup? do we need to update anything the documentation related to the setup?
https://github.com/ARMmbed/mbed-os/blob/master/TESTS/usb_device/README.md

[fkjagodzinski]

@jamesbeyond, no impact on the setup procedure.

This patch explicitly sets the pyusb backend to libusb0 to make sure we always use the driver set by Zadig. If the user has libusb1 present in Win environment, it will be loaded by default by pyusb. This is bad, since this lib version does not provide all features we use in tests.

[adbridge]

@jamesbeyond are you happy with this ?

[jamesbeyond]

I am happy, good to go @adbridge

[adbridge]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 4 of 4 test jobs passed
Build number : 1
Build artifacts