Improving vtkExodusIIReader and adding a test.

Changing some array names, updating comments and adding a
test to check side set source information.

Change-Id: Id65e24aa887666799dda6a63ce443135a3aae02c
Merge topic 'exodusreader_side_set_info' into master

b64b8a66 Improving vtkExodusIIReader and adding a test.