User registration and password reset are broken due to the last_authenticated value being null

[srijeet0406]

This Bug Report affects these Traffic Control components:

• Traffic Ops
• Traffic Portal

Current behavior:

In Traffic Portal, try registering a new user, or resetting the password of an existing user. You'll notice that the operation fails. If you tail the logs, you'll see something similar to:
getting current user: querying current user: sql: Scan error on column index 9, name "last_authenticated": unsupported Scan, storing driver.Value type <nil> into type *time.Time

Expected behavior:

Registration/ password reset should work as expected.

Steps to reproduce:

In Traffic Portal, try registering a new user, or resetting the password of an existing user.