BUG/ERR: raise on saving a multi-index with tz-info in fixed format for HDF5

[jreback]

xref: #8165
http://stackoverflow.com/questions/24805307/losing-timezone-awareness-when-saving-hyerarchical-pandas-datetimeindex-to-hdf5/24805506#2480550

should raise NotImplementedError for now, or actually implement

[jreback]

cc @mroeschke