Making datetime timezone aware in CW module and adding security token in Redshift

[jaidisido]

Description of changes:

• Datetime method needs to be UTC timezone aware, otherwise datetime.datetime(year=1970, month=1, day=1) will return a different timestamp value (potentially negative) depending on the user's timezone
• Set security token explicitly in Redshift test file

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.