`load_hdf5()` filename issues

[kwmsmith]

If Context.load_hdf5() is called with a relative path, it may fail with an:

IPython.parallel.error.CompositeError: one or more exceptions from call to method: func_wrapper
[0:apply]: IOError: Unable to open file (Mpi_err_no_such_file: no such file or directory)
[1:apply]: IOError: Unable to open file (Mpi_err_no_such_file: no such file or directory)
[2:apply]: IOError: Unable to open file (Mpi_err_no_such_file: no such file or directory)
[3:apply]: IOError: Unable to open file (Mpi_err_no_such_file: no such file or directory)

No error results if an absolute path is passed in instead.

I'd like to see Context.load_hdf5 detect relative paths client-side and resolve into absolute paths before passing to engines, which should resolve this issue.

[markkness]

What if Context.load_hdf5 always called os.path.abspath() on its filename, to ensure an absolute path? Then it wouldnt have to explicitly detect anything.

[bgrant]

One problem here: We've agreed that for these functions, the client might not have access to the same filesystem as the engines.

The choice I originally made here was to pass the filename directly to h5py.File and let h5py handle filenames however it normally handles them. I can see how this is confusing though.