Add 'explain' command to v2 that describes schemas

At its core, this is adding the ability to finx a schema through
published links and convert it to a usable object.

Related to bp glance-client-v2

Change-Id: I7b38ad091c6b0ad80197eb789503cf73989893e5

glanceclient/v2/shell.py

@@ -21,3 +21,11 @@ def do_image_list(gc, args):
     images = gc.images.list()
     columns = ['ID', 'Name']
     utils.print_list(images, columns)
+
+
+@utils.arg('name', metavar='<NAME>', help='Name of model to describe.')
+def do_explain(gc, args):
+    """Describe a specific model."""
+    schema = gc.schemas.get(args.name)
+    columns = ['Name', 'Description']
+    utils.print_list(schema.properties, columns)