Change return value of Schema::childNodes

I'll need to use this method to generate what can be parsed as paths in
the upcoming path parser rework. As a side effect, path completion
generation gets a little bit simpler, because now I don't have to parse
the strings of format "[module:]node" and just trust whatever the schema
gives me.

Change-Id: I881cdbbd8254b846c21cee1ac0a3b7af1e40a696
diff --git a/tests/ls_interpreter.cpp b/tests/ls_interpreter.cpp
index 6b02d80..a78194e 100644
--- a/tests/ls_interpreter.cpp
+++ b/tests/ls_interpreter.cpp
@@ -149,6 +149,6 @@
     REQUIRE_CALL(datastore, schema()).RETURN(schema);
     ls_ ls;
     ls.m_path = lsArg;
-    REQUIRE_CALL(*schema, availableNodes(expectedPath, Recursion::NonRecursive)).RETURN(std::set<std::string>{});
+    REQUIRE_CALL(*schema, availableNodes(expectedPath, Recursion::NonRecursive)).RETURN(std::set<ModuleNodePair>{});
     Interpreter(parser, datastore)(ls);
 }