test/pybind/rbd: convert from nose to pytest

test/pybind/rbd: convert from nose to pytest

* use fixtures for temporary images and groups
* use pytest.skip instead of nose.SkipTest
* replace setUp/tearDown with setup/teardown_method
* add @pytest.mark.skip_if_crimson
* replace nose assertions

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit af04457a43921bcac85b572098245a4c8a79452e)

Conflicts:
	qa/suites/crimson-rados/rbd/tasks/rbd_python_api_tests.yaml
		does not exist on quincy
	qa/suites/crimson-rados/rbd/tasks/rbd_python_api_tests_old_format.yaml
	qa/workunits/rbd/test_librbd_python.sh
	src/test/pybind/test_rbd.py
		skip_if_crimson filter not present on quincy