Add tests for super_key.rs

The new tests are focused on unlocking, resetting and removing a user.
The tests verify that keys are deleted when necessary and that the user
state transitions properly.

Bug: 280502317
Test: atest keystore2_test on cuttlefish
Change-Id: Idae5d99fb289045bb277ba6c93ab62cfd9aed6fb
diff --git a/keystore2/src/legacy_importer.rs b/keystore2/src/legacy_importer.rs
index 9eb702d..325c213 100644
--- a/keystore2/src/legacy_importer.rs
+++ b/keystore2/src/legacy_importer.rs
@@ -102,6 +102,11 @@
         }
     }
 
+    #[cfg(test)]
+    pub fn set_empty(&mut self) {
+        self.state = AtomicU8::new(Self::STATE_EMPTY);
+    }
+
     /// The legacy importer must be initialized deferred, because keystore starts very early.
     /// At this time the data partition may not be mounted. So we cannot open database connections
     /// until we get actual key load requests. This sets the function that the legacy loader