[gpuCI] Clear stale CMake files and report failures.

[alliepiper]

I noticed that gcc-5 has been failing for some time, but was reported as passing. This is because the build failures were in CUDA targets, but only non-CUDA tests are run on the cpu testers and the builder would only fail if the testing step failed.

Now it checks the configure, build, and test steps explicitly and logs a summary of which steps failed at the end of the output. Now gcc-5 reports as failing:

>>>> Summary:
>>>> - Configure Error Code: 0
>>>> - Build Error Code: 1
>>>> - Test Error Code: 0

[alliepiper]

run tests

[alliepiper]

@brycelelbach this fixes the build script so that gcc-5 now shows as failing. We were missing these because the tests still passed, even though there were build errors.