BUG/TST raise a more detailed error when GH6169 occurs, added a test

Raise a detailed error when a `columns` argument is passed through 'where' to
select a multiIndexed Dataframe from an HDF store. Wrote a test
showcasing the bug

	modified:   pandas/io/pytables.py
	modified:   pandas/io/tests/test_pytables.py

making it work
BUG: correctly select on a multi-index even in the prescence of under specificed columsn spec (GH6169)
Merge pull request #6202 from jreback/mi_hdf

BUG: correctly select on a multi-index even in the prescence of under specificed column spec (GH6169)