BUG-8372: add dataTree information

We are attempting to send a local message to a remote actor,
which seems to be a mixup with data tree presence. Add dataTree
to toString() output so we know which connections resolve to
being local and which to being remote.

Change-Id: If1ed3cfdea24148456a4d310949fb480791c1ffa
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit 3f8818fd65f1cac8f4b2ce3b7319255137c74da5)