Add testing consumer_cmd executable

Mostly a stub to unblock the work on the CTS test and for
local tests. Some work left to do w.r.t. importing the
trace config from stdin and producing some more meaningful
outut.
Also, makes a minor change to the API surface that returns
the vector<TracePacket> by value (allowing to std::move it)
rather than passing a const ref, that makes the API hard to
use.

Change-Id: Iccf88b7b1d2beb6a0750adafd86d92a0f563182d
diff --git a/src/tracing/ipc/service/consumer_ipc_service.h b/src/tracing/ipc/service/consumer_ipc_service.h
index ad6e203..42466b3 100644
--- a/src/tracing/ipc/service/consumer_ipc_service.h
+++ b/src/tracing/ipc/service/consumer_ipc_service.h
@@ -67,7 +67,7 @@
     // no connection here, these methods are posted straight away.
     void OnConnect() override;
     void OnDisconnect() override;
-    void OnTraceData(const std::vector<TracePacket>&, bool has_more) override;
+    void OnTraceData(std::vector<TracePacket>, bool has_more) override;
 
     // The interface obtained from the core service business logic through
     // Service::ConnectConsumer(this). This allows to invoke methods for a