Rendering engine plugins not loaded on Windows

**Original report ([archived issue](https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-rendering/issues/40)) by Ian Chen (Bitbucket: [Ian Chen](https://bitbucket.org/%7Beaa6fca5-6deb-43f6-907f-971c144735dd%7D/), GitHub: [iche033](https://github.com/iche033)).**

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When tests are runs on jenkins, the rendering plugins are not found and prints out this msg:

```
1: [Err] [d:\jenkins\workspace\ign_rendering-ci-win\ws\ign-rendering\src\renderenginemanager.cc:268] Failed to load plugin [ignition-rendering0-ogre] : couldn't find shared library.
```

It could be a path problem