BAU: Fix timezone issue
BAU: Fix timezone issue

Verify frontend is comparing notOnOrAfter field (assertion_expiry)
against the current system clock. The clock can be in different timezone
e.g. British Summer Time (GMT+0100). According to SAML specification,
notOnOrAfter specifies the time instant at which the assertion has
expired. The time value is encoded in UTC. This commit updates verify
frontend to compare notOnOrAfter field against the system clock in UTC.
This will prevent users from getting session timeout errors.

Author: da39a3ee5e6b4b0d3255bfef95601890afd80709@adityapahuja

alphagov/verify-frontend,alphagov/verify-frontend,alphagov/verify-frontend,alphagov/verify-frontend