sdbus++: Prepend all errors with 'Error' namespace

Old:
    Error identifier: com.example.Interface.LogicError
    Exception class: com::example::Interface::common::LogicError

New:
    Error identifier: com.example.Interface.Error.LogicError
    Exception class: com::example::Interface::Error::LogicError

Change-Id: I866046f4a0514f5bce40bdef46a218060d107765
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/tools/example/net/poettering/Calculator.interface.yaml b/tools/example/net/poettering/Calculator.interface.yaml
index 4167c36..3c70cbc 100644
--- a/tools/example/net/poettering/Calculator.interface.yaml
+++ b/tools/example/net/poettering/Calculator.interface.yaml
@@ -40,7 +40,7 @@
           description: >
             The result of (x/y).
       errors:
-        - self.DivisionByZero
+        - self.Error.DivisionByZero
     - name: Clear
       description: >
         Reset the LastResult property to zero.