Qbs: Move build step connection setup to build step constructor

Instead of doing it manually afterwards on both paths that create
them.

Change-Id: I0e1734ae2b5028ce1d471aea0272df52acead221
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qbsprojectmanager/qbsbuildstep.cpp

@@ -128,6 +128,11 @@ QbsBuildStep::QbsBuildStep(ProjectExplorer::BuildStepList *bsl) :
     setDisplayName(tr("Qbs Build"));
     setQbsConfiguration(QVariantMap());
 
+    auto qbsBuildConfig = qobject_cast<QbsBuildConfiguration *>(buildConfiguration());
+    QTC_CHECK(qbsBuildConfig);
+    connect(this, &QbsBuildStep::qbsConfigurationChanged,
+            qbsBuildConfig, &QbsBuildConfiguration::qbsConfigurationChanged);
+
 //    setQbsConfiguration(other->qbsConfiguration(PreserveVariables));
 }