[Ogre1.x] GpuRays integration tests are failing on homebrew

**Original report ([archived issue](https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-rendering/issues/35)) 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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Jenkins homebrew job caught two test failures:

`GpuRays/GpuRaysTest.RaysUnitBox/ogre`

`GpuRays/GpuRaysTest.LaserVertical/ogre`

In gazebo, the `LaserVertical` test is disabled for macOS so that's a known issue but `RaysUnitBox` should pass.

Output from jenkins below:

GpuRays/GpuRaysTest.RaysUnitBox/ogre

```
/Users/jenkins/workspace/ignition_rendering-ci-pr_any-homebrew-amd64/ign-rendering/test/integration/gpu_rays.cc:248
The difference between scan[mid] and expectedRangeAtMidPointBox1 is 2.5, which exceeds 1e-4, where
scan[mid] evaluates to 0,
expectedRangeAtMidPointBox1 evaluates to 2.5, and
1e-4 evaluates to 0.0001.
```

GpuRays/GpuRaysTest.LaserVertical/ogre

```
/Users/jenkins/workspace/ignition_rendering-ci-pr_any-homebrew-amd64/ign-rendering/test/integration/gpu_rays.cc:382
The difference between scan[i * hRayCount * channels + mid] and expectedRange is 0.094709730238659473, which exceeds 1e-3, where
scan[i * hRayCount * channels + mid] evaluates to 0.25884366035461426,
expectedRange evaluates to 0.35355339059327373, and
1e-3 evaluates to 0.001.
```