[python-muranoclient] importing package by url

In order to support cataloguing of packages on external resources we need to allow importing packages by url. To do this with CLI tools like "murano package-import http://path.to/package" few changes have to be made to the python-muranoclient: support for addittional parameter to the `package-import` subcommand. It is also viable to allow it to distinguish between local file-path and url, choosing which action to take based on the format of the string supplied.