Fix timezones in certificate revocation list dates

While generating certificate revocation list, dates were generated with
an incorrect TZ information. Depending on the TZ of host, some tests
failed because last update was in the future.

Using datetime.utcnow() for dates fixes the issue.

Change-Id: I2ff30c1a65e07b409aba211d1c60760355bfebbe
1 file changed