When a store is encrypted symmetrically, and no passphrase is in context, it should default to asking passphrase

[oleiade]

I've noticed that when you have no passphrase in your context (keyring, environment, etc...), trousseau raises an error. I would expect it to ask me for a passphrase instead. I think the scope of this issue is implementing the following:

1. If not passphrase in context, ask for it interactively.
2. Add a --no-interactive global option to forbid this sort of behaviors (to make scripting easier).