bindings: python: fix package installation with Makefile build

The modules are installed in the .egg directory, and therefore cannot be
imported after that. Additionally PIP tries to remove the global gpiod
module if it's not invoked with the --ignore-installed option.

Specify correct --root and fix the --prefix switch.

Link: pypa/pip#3063
Suggested-by: Maxim Devaev <mdevaev@gmail.com>
Reported-by: Maxim Devaev <mdevaev@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

bindings/python/Makefile.am

@@ -36,7 +36,7 @@ all-local: python-tests
 
 install-exec-local:
  $(PYTHON) -m pip install dist/*.whl \
- --prefix=$(DESTDIR)$(prefix)
+ --ignore-installed --prefix=$(prefix) --root=$(if $(DESTDIR),$(DESTDIR),/)
 
 SUBDIRS = gpiod