FIX - test_dccnpath to run in the DCCN cluster

[contsili]

This PR is related to #2298 and contsili#6.

For now, the dccnpath we have developed works hierarchically. It first uses alternative0 and if the file exists then dccnpath stops (using the MATLAB command return). If alternative0 doesn't lead to a file that exists, then dccnpath uses alternative1, and finally alternative2 in the same way.

So, for all the DCCN cluster computers, alternative0 should always work since the files are pre-downloaded to these computers. As a result, test_dccnpath will not work properly when testing alternative1 and alternative2 inside the DCCN computer cluster.

I made corrections to test_dccnpath, so it will now work properly in the DCCN desktops and in the HPC cluster.

Note: another way to overcome this issue is to replace if ~startsWith(filename, tmpdir) with if ~exist(filename, 'file') / if ~exist(filename, 'dir') for alternative1 and alternative2-test1 in test_dccnpath. But in this case our if statement becomes a bit more general than what we try to test.

[robertoostenveld]

If, on a compute node, I specify ft_default.dccnpath to be something different, then that must be used. Also, if on a compute node, the file exists in the present working directory, that file must be used. Either one might for example happen with a new or updated test for which the corresponding data has not yet been copied to the standard location.

So in those cases alternative0 is skipped and alternative1 or alternative2 are used.

[robertoostenveld]

I agree that an extra check is in place prior to deleting the temporary directory. We don't want any intermediate/undetected change of ft_default.dccnpath to cause another directory to be deleted.

[robertoostenveld]

I realize that alternative 0 takes precedence over 1 and 2, so the user is technically not able to specify on the compute cluster where the data is. I suppose that is what you mean...

I do think that the desired (i.e., perfect) behavior is what I described above: the user is in charge of determining which file is to be read. However, for now it is not important enough to rewrite dccnpath again to accommodate this, as an FT contributor who works on the DCCN cluster is likely to be me or @schoffelen anyway, and we know how it works and/or will find a workaround. So let's not make it perfect, I believe it is good enough already.

Your change to the test script (making it conditional on where it runs) is therefore appropriate.