homed: rename home_prepare*() → home_setup*()

homed: rename home_prepare*() → home_setup*()

These set of functions are constructors for an object called HomeSetup,
which has a destructor home_setup_undo(), hence to be reasonably
symmetric, let's call it home_setup*() too, instead of using a new verb
"prepare" for its name.

No actual code changes, just some renaming.