ConnectivityManager: uses service error codes and exceptions

This patch introduces between ConnectivityManager and
ConnectivityService a mechanism for propagating back to clients
informative errors in the form of error codes and associated custom
runtime exceptions.

Without error code, the service can only throw a limited number of
different exceptions over Binder. Furthermore the throw site stack
traces are always loss. Although for individual instances of a throw,
the error message can be inspected, aggregations of stack traces from
app crashes sanitize error messages and only leaves the stack traces.

This makes debugging dificult for some service calls such as
requestNetwork that can have a variety of failure modes.

In this patch only one failure mode is codified. More can be added later
at a light cost by: 1) defining an error code, 2) defining an
associated exception, 3) mapping the code to the exception. This patch
can serves as a template for doing so.

Test: $ runtest frameworks-net,
      #testNetworkRequestMaximum() detects the new exception type.
Bug:  36556809, 36701874
Change-Id: I611fd7915575c9e418f7149fcdc8a879d2a3716d