Unskip and fix DAP tests.
Remove owner_ related calls from client.
Fix a Python 3 incompatibility.
Fix an error in how 'gridrank' keys are set.

The error was that 'rank' was being used instead of the proper index of 'cart_rank' for each dimension.
Fix __getitem__ and __setitem__ in client.

Warning: a a bit hacky.
Fix some python 3 incompatibilities.

`x.next() -> six.next(x)`
and `mydict.items() -> list(mydict.items())`
Remove an unused import.