[DataHandleProvider] Adapt to upstream changes in PDELab

PDELab commits d750a64449cb01f8cc0e668de135d771a772f096 and
f6585524de4c88158dfb8baceab13c23a6ae947a changed the way the
DataHandleProvider handles GFS size information. This patch contains the
corresponding changes at the MultiDomain level.
[Git] Ignore parallel VTK output files