cmd/relui: correct database configuration
cmd/relui: correct database configuration

Add missing IAM flag for cloud_sql_proxy, and use the correct user and
database in relui environment.

For golang/go#47401

Change-Id: I2fa760c00f7000552d87069f259750fa455cce92
Reviewed-on: https://go-review.googlesource.com/c/build/+/363695
Trust: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Run-TryBot: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/build,golang/build,golang/build,golang/build