In previous commits, we added the ability to specify which UID we want to target on certain operations. This commit adds the ability to reach those binder calls from the KeyStore class. Also fix a problem where saw() was not reading all the values returned via the Binder call. This changes the semantics to return a null instead of failing silently when it's not possible to search. Change-Id: I32098dc0eb42e09ace89f6b7455766842a72e9f4