Sync breaks when the host's user's shell is set to /usr/bin/nologin (or /usr/bin/false)

[eriknelson]

As I mentioned in #1949, I pre-created a "system" account. It's common to set their shell to /usr/bin/nologin, or /usr/bin/false. However, Sparkleshare's ssh comms immediately close their connection from clients if this is configured.

1. Curious if it would even be possible to support these types of nologin shells for the host's user? (I'm guessing the answer is probably not).
2. If that's not an option, does the project have an "installation" section of documentation where it makes sense to document this as a requirement?