Redefine the structure of the CalcInfo.local_copy_list

[sphuber]

Fixes #2573

With the upcoming change of the node repository, files within it can no
longer be assumed to necessarily be stored on the local file system. It
is therefore impossible to address files within it through an absolute
file path, however, that is exactly what the local_copy_list expects
as the first item of its tuples.

Now, the Node class only exposes methods to get either the content of
a repository file or an filelike object. To comply with this change in
design the structure of the local_copy_list tuples is changed to
tuples of length three where each element represents:

• UUID of the node
• Relative key of the file within the node repository
• Relative path within the working directory where to copy the file

The upload_calculation function of the execmanager has been updated to
this interface change, but because our Transport interface does not
yet provide a method to put an object from a filelike object, we have to
create a temporary file on the local file system whose absolute filepath
can be passed to the Transport.put call. Once the transport is updated
to provide a put_object_from_filelike, this inefficiency can be removed.

[sphuber]

@ltalirz and @yakutovicha if this PR gets merged, we need to update the guide for the implementation of CalcJob classes. After this fix, for a given node, to copy one of the files in its repositories, one can do:

folder = self.inputs.folder # FolderData
singlefile = self.inputs.single # SinglefileData
local_copy_list = [
    (folder.uuid, 'relative/path.txt', 'relative/destination.txt')
    (single.uuid, single.filename, 'input_file.upf')
]

[sphuber]

The failing test on Jenkins is a known bug that Casper is addressing in PR #2576

[coveralls]

Coverage increased (+0.01%) to 70.051% when pulling 4976712 on sphuber:fix_2573_redefine_local_copy_list into 277a4d8 on aiidateam:provenance_redesign.