Implement keystore2 logging of key creation events.

This CL implements logging of key creation events via statsd.

Bug: 172013262
Test: enable keystore2 on cuttlfish, run cts tests for key generation,
run the test drive script provided by statsd and observe the logs
created.

Change-Id: Ib60ed356ce809d27f7625ab0743a9300c454f1c8
diff --git a/keystore2/src/lib.rs b/keystore2/src/lib.rs
index cb47e3e..7ece6fa 100644
--- a/keystore2/src/lib.rs
+++ b/keystore2/src/lib.rs
@@ -28,6 +28,7 @@
 pub mod legacy_blob;
 pub mod legacy_migrator;
 pub mod maintenance;
+pub mod metrics;
 pub mod operation;
 pub mod permission;
 pub mod remote_provisioning;