Exception thrown in runAllTests

[k1o0]

The following exception is thrown occasionally, after all the tests have successfully completed:

Done Alyx_test
__________

Tearing down PathFixture
Done tearing down PathFixture: Restored the path to its original state.
__________

Error in 'mustContainCharacters' line 13: MATLAB:unittest:StringInputValidation:InvalidValueMustContainCharacters: 
Invalid 'file' value. Input must contain one or more characters.

The error is mostly thrown by fileread or fopen, however the filename itself is constant so getting this error only some of the time is confusing.

For now I've added a line to print the full stack.

Also this line causes an error when the file doesn't exist:
https://github.com/cortex-lab/matlab-ci/blob/98bf56eb540631969e755b7d2ee98004f7b3604a/runAllTests.m#L56-L57

[k1o0]

Solved: this occurs when the git checkout removes some files that are still in MATLAB's file cache. This will be resolved if we reset the paths each time (see #18)