Use unique temporary filename for keystore blob.

If the writeBlob is invoked by concurrent threads, the temporary
file can be deleted before the write operation completes.

Bug: b/115688924
Test: atest keystore_unit_tests
Test: atest KeystoreTests
Test: atest cts/tests/tests/keystore/
Change-Id: Icdadacc9af4af281bff6fc17a6b43ba731377b53
1 file changed