Keep escrow data for test users

For normal unmanaged users escrow data is destroyed when the user
authenticates successfully. This makes such a user unusable for password reset tests.

Bug: 397357492
Test: atest FrameworksServicesTests:com.android.server.locksettings
Flag: EXEMPT bugfix

Change-Id: I451a778a4208c6a50592bc5df88f65991fa727aa