adduser should invoke with --create-home even if password is None

[Adam Israel]

We've hit cases where we want to add a user to the system, without a password (for system services or to use ssh keys for authentication) but still require a home directory. The current behavior skips this flag if the password is None.

adduser should either use the --create-home flag when no password is present, or expose an additional flag to the developer to use the flag on demand.