Fix malformed config if no passphrase set

[strugee]

The problem is that if there's no passphrase set, the role will generate this config:

storage:
    encryption_passphrase: 

    [etc.]

but Borgmatic errors out on this config with a message about None not being a string. I considered doing {{ borg_encryption_passphrase or "''" }} but it seemed cleaner to just omit the value entirely. Upstream's default is '' FWIW. I tested this patch in production and borgmatic create successfully runs with it.

[m3nu]

Thanks! That's a sensible improvement.

[strugee]

Much appreciated! Any plans to cut a release soon? If not I'll try and figure out how to pin directly to a commit