Change ICommonClock marshallers to return explicit error codes.

Change the ICommonClock marshallers to return an explicit error with
each transaction.  This makes it easier to disambiguate between binder
errors (dead object due to the service crashing) vs. runtime errors
(cannot return common time due to lack of sync)

Change-Id: I2182cf0cfb2e11b4669f392554f104ef7c4bca8b