RemoteLinux: Deployment improvements.

- Don't depend on the order of signal connections when updating the
deploy step label.
- Give a meaningful error message when the init() function fails.
- Don't try to upload files that don't have a target path set.

Change-Id: If302cf8407b69faf8507579267afde7428edf704
Reviewed-on: http://codereview.qt-project.org/5404
Reviewed-by: Christian Kandeler <christian.kandeler@nokia.com>

src/plugins/remotelinux/abstractremotelinuxdeploystep.cpp

@@ -78,7 +78,11 @@ QVariantMap AbstractRemoteLinuxDeployStep::toMap() const
 
 bool AbstractRemoteLinuxDeployStep::init()
 {
-    return isDeploymentPossible();
+    QString error;
+    const bool canDeploy = isDeploymentPossible(&error);
+    if (!canDeploy)
+        emit addOutput(tr("Deployment failed: %1").arg(error), ErrorMessageOutput);
+    return canDeploy;
 }
 
 bool AbstractRemoteLinuxDeployStep::isDeploymentPossible(QString *whyNot) const