Revert "Revert "TST: Log scale on bar chart hides bars GH3247" mpl 1.2.1 regression"

This reverts commit fc355b1fb95e78bf004d10cb7f2a2114399508a1.
BUG: work around mpl 1.2.1 regression, bar(log=True,bottom=None)) GH3254
BUG: work around mpl 1.2.1 regression,  ax.axhline(0) with log=true GH3298
Merge pull request #3300 from y-p/log_bar

Work around mpl 1.2.1 regression re bar log plot GH3298, GH3254