Keystore 2.0: Move test utils to separate library.

Move TempDir test utils to separate library for easier reuse.

Test: keystore2_test
Change-Id: If1edfde39b66efa43f8a5ed32a500fad57291512
diff --git a/keystore2/src/legacy_blob.rs b/keystore2/src/legacy_blob.rs
index 34a0eca..230a82c 100644
--- a/keystore2/src/legacy_blob.rs
+++ b/keystore2/src/legacy_blob.rs
@@ -775,7 +775,7 @@
     mod legacy_blob_test_vectors;
     use crate::error;
     use crate::legacy_blob::test::legacy_blob_test_vectors::*;
-    use crate::test::utils::TempDir;
+    use keystore2_test_utils::TempDir;
 
     #[test]
     fn decode_encode_alias_test() {