EncryptedServerSideMultipartManagerIT#doubleCompleteFails causes its own error (incorrectly)

[tjcelaya]

This test case asserts that an exception is thrown when EncryptedServerSideMultipartManager#complete is called twice but that's not actually what it's testing. The IllegalStateException is throw because partStream has already been consumed, replacing the variable with Arrays.stream(parts) prevents the exception.