Keystore 2.0: Add watch dog library.

Add keystore watchdog thread to monitor keystore code paths for
unusually long execution time.

Bug: 184006658
Test: keystore2_test
Change-Id: I942e3c736725ac41bcef43b9da43800ef773e7b5
diff --git a/keystore2/src/lib.rs b/keystore2/src/lib.rs
index 3332b83..11af9df 100644
--- a/keystore2/src/lib.rs
+++ b/keystore2/src/lib.rs
@@ -47,3 +47,4 @@
 mod db_utils;
 mod gc;
 mod super_key;
+mod watchdog;