Fixes an issue where all OpenCL tests passed irrespective of whether they are right or wrong

The old test runner implementation also ran the reference operation for the OpenCL version. It was identified that the environment variable was not set correctly, and this merge request addresses that issue.

However, the current version still has some problems. Notably, it does not verify that the test uses the OpenCL implementation instead of the reference implementation. This failure has been observed in gblur-1d, where the default filter selected for the test image is IIR, which has no OpenCL implementation, while the FIR implementation does have an OpenCL version. It has also been observed in edge-sobel, where the OpenCL version has been disabled.

The current patch fixes all tests where operations have an exclusive OpenCL version.