Fix cross-user content resolver tests.

Wait for the user to get unlocked before trying to start an
encryption-unaware app in that user.

Fixes: 69927817
Test: adb shell am instrument -e class android.content.ManagedUserContentResolverTest -w
      com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Change-Id: I36f38d20c7f4584a68bc3b1b99941ce3e3b3815c