Test that the password isn't truncated

Test that Gatekeeper doesn't truncate passwords, either due to them
containing NUL bytes or being long.

Bug: 238919794
Test: atest VtsHalGatekeeperV1_0TargetTest # on Cuttlefish
Change-Id: I8dd40c66bbe5cd8d309a6461053389b479fa0745