Avoid TypeError in is_older_than, is_newer_than

datetime doesn't like to subtract offset-naive and
offset-aware datetimes. To fix this we convert all
datetimes that are passed in to offset-naive objects.

Change-Id: Ib01568c9d287e319750b6bef3656fdcfc992a1b1
Closes-Bug: #1259383
Merge "Avoid TypeError in is_older_than, is_newer_than"