[k8s plugin] Kubernetes: Run/Debug commands can't locate a project's Dockerfile

[azatsarynnyy]

Steps to reproduce:
1/ Create a Workspace from the Devfile https://github.com/azatsarynnyy/devfiles/blob/master/k8s-devfile.yml
2/ Inject your local kubeconfig into the running Workspace with chectl workspace:inject and refresh the browser's page
3/ Call the Kubernetes: Run or Kubernetes: Debug command

The command is failed with the error:
error reading info about "/projects/projects/Dockerfile": stat /projects/projects/Dockerfile: no such file or directory

The command tries to find a Dockerfile in nonexistent /projects/projects folder instead of /projects/simple-nodejs-weather-app folder.

[azatsarynnyy]

Kubernetes: Run command tries to find a Dockerfile into Theia workspace root folder which is /projects by default.
Since /projects is a parent folder for all of the projects in Che Workspace, in order to use Kubernetes: Run command the user needs to open a particular folder as a Theia workspace root folder with File > Open Workspace... menu item. After that step, an image build is starting successfully.