TST/ERR: raise a ValueError at runtime for incompatible versions of openpyxl

instead of warning at import time

add openpyxl 2.0.3 to trigger travis fails on import
Merge pull request #7285 from cpcloud/openpyxl-format-string-fix-7284

BUG/CI/TST: fix format strings
ENH: Add dateutil timezone support GH4688

Adds support for dateutil timezones across pandas.
Support conversion between dateutil and pytz timezones.
Ensure timezone functionality is tested with both dateutil and pytz.