883486: The local time's start/end dates rendered in the list --available/--consumed incorrect

Dates displayed were shifted based on machine's DST/EST state instead of the state
on the actual date getting formated.

Altered the timezone calculation to use standard python packages instead of
our own incorrect implementation.
Use dateutil.tz instead of pytz.
Merge pull request #871 from candlepin/wottop/883486

883486: The local time's start/end dates rendered in the list --availabl...