shill: Framework for asynchronous service side RPC calls.

Use the framework to switch EnterPIN to return asynchronously.

Also, added a few try/catch clauses around DBus proxy calls to ease testing and
debugging. They should go away as we transition to asynchronous proxy calls.

BUG=chromium-os:17263
TEST=unit tests, tested on device

Change-Id: I4177c5b91e23c31838b03689de729932c859a936
Reviewed-on: https://gerrit.chromium.org/gerrit/12541
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Eric Shienbrood <ers@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/mock_adaptors.cc b/mock_adaptors.cc
index 61881e5..7634dfb 100644
--- a/mock_adaptors.cc
+++ b/mock_adaptors.cc
@@ -61,4 +61,9 @@
 ServiceMockAdaptor::~ServiceMockAdaptor() {}
 
 const std::string &ServiceMockAdaptor::GetRpcIdentifier() { return rpc_id; }
+
+MockReturner::MockReturner() {}
+
+MockReturner::~MockReturner() {}
+
 }  // namespace shill