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
11 files changed