BUG: multi-index with one level with a tz buggy

[jreback]

related: #7791, #7792 (and I think this causes both)
this is a dupe of #7746

In [8]: df = DataFrame(np.arange(6).reshape(6,1),index=MultiIndex.from_product([['a','b'],date_range('20130101',periods=3,tz='Europe/Berlin')]))

In [9]: df
Out[9]: 
                             0
a 2013-01-01 00:00:00+01:00  0
  2013-01-02 00:00:00+01:00  1
  2013-01-03 00:00:00+01:00  2
b 2013-01-01 00:00:00+01:00  3
  2013-01-02 00:00:00+01:00  4
  2013-01-03 00:00:00+01:00  5

In [10]: df.reset_index()

ValueError: Length of values does not match length of index

[jreback]

xref #7792

cc @sinhrks