Re-structured keystore test-utils module.

- Created separate build file.
- Moved ffi-utils from keystore2-client-tests to test-utils.
- Updated calling apis.

Test: atest keystore2_client_tests; atest keystore2_test_utils_test;
atest keystore2_test
Bug: 194359114

Change-Id: Ia2404218b7d13a9ae43b3fc4e481899576d24e63
diff --git a/keystore2/test_utils/lib.rs b/keystore2/test_utils/lib.rs
index c63bfac..a373a2f 100644
--- a/keystore2/test_utils/lib.rs
+++ b/keystore2/test_utils/lib.rs
@@ -22,6 +22,7 @@
 use android_system_keystore2::aidl::android::system::keystore2::IKeystoreService::IKeystoreService;
 
 pub mod authorizations;
+pub mod ffi_test_utils;
 pub mod key_generations;
 pub mod run_as;