Fix for V2 token issued_at time changing

When the server converted a V2 token to a V3 token it regenerated
the issued_at time.

This was causing the server to return a different issued_at time
when a V2 token was validated using the V3 API.

This was causing the server to fail to revoke a V2 token if it was
revoked before validating it first because the regenerated token was
considered to be after the revocation event.

Change-Id: I71fea3253295ee8794fb2c8211e1f030de3ae205
Closes-Bug: #1348820
(cherry picked from commit a4c73e4382cb062aa9f30fe1960d5014d3c49cc2)