RemoteLinux: Use a structure to return check results

Instead of the combined bool value + QString * out parameter.

Change-Id: I8840f48b74aaacd1b0c0412efd8abcdc2be12d58
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/remotelinux/remotelinuxcustomcommanddeployservice.h

@@ -41,7 +41,7 @@ public:
     void setCommandLine(const QString &commandLine);
 
     bool isDeploymentNecessary() const override { return true; }
-    bool isDeploymentPossible(QString *whyNot = nullptr) const override;
+    CheckResult isDeploymentPossible() const override;
 
 protected:
     void doDeviceSetup() override { handleDeviceSetupDone(true); }