Set a default user openrc file

[Peter Matulis]

When deploying a single-node (guided) or a multi-node cloud the cloud is configured with:

$ sunbeam configure --openrc demo-openrc

It seems that the user should not need to specify the cloud init file - a default can be set such as 'user-openrc' (to distinguish it from an admin file like 'admin-openrc').

Same thing for obtaining an admin init file. Instead of:

$ sunbeam openrc > admin-openrc

Maybe just:

$ sunbeam openrc

I realise that this changes the STDOUT mechanism.

Do we want a generic init file generator instead?

$ sunbeam create-init --user
$ sunbeam create-init --user --file ubuntu-openrc
$ sunbeam create-init --admin
$ sunbeam create-init --admin --file admin-openrc