chg: dev: Use realpath for pytest plugin search paths
chg: dev: Use realpath for pytest plugin search paths

Starting on pytest 3.9.2 pytest resolves symbolic links:
https://github.com/pytest-dev/pytest/pull/4108/

This causes an uncompatibility with the attribute injection feature
as the paths pytest sees (realpaths) differ from the injected_attr
(abspath) found on the topology_plugin.

HPENetworking/topology