cli: Fix the default image name

Two things:

• Don't duplicate the image name (so it becomes repo.fqdn/tool_user/image_name:tag instead of repo.fqdn/tool_user/image_name/image_name:tag). If/when we want to start supporting subrepos for each tool we can change that, for now maintain-harbor does not create those subrepos so we can't easily use them.
• Use the current user to get the base image name instead of the current directory, so when you have done a 'cd' inside a directory, it will not change the image name.

Note that with this if you want more than one image for your tool, the
only difference is going to be the image name, not the subrepository.

Bug: T324824
Change-Id: I4fe7a1bfe87d44d993eacd4ead833d642133ff80