[Blueprints] ensure git:directory resource returns non-empty-name

[adamziel]

Motivation for the change, related issues

Before this PR, this step would fail:

{
		"step": "installPlugin",
		"pluginData": {
			"resource": "git:directory",
			"url": "https://github.com/juanma-wp/meetup-cheltenham-workshop/",
			"ref": "final",
			"path": "/"
		},
		"options": {
			"activate": true
		}
},

This is because installPlugin names the plugin directory inside wp-content after the filename of the resolved resource, and the git:directory resource would use path to generate a filename called /.

With this PR, git:directory generates a directory name using the full set of information from the resource spec: URL, ref, path. The names are now more like this: https-github.com-WordPress-wordpress-playground-trunk.

Testing Instructions (or ideally a Blueprint)

CI – this PR comes with tests

cc @juanmaguitar