CheckResults: pass IServer to sharemap=, but get_sharemap() returns serverids

CheckResults: pass IServer to sharemap=, but get_sharemap() returns serverids

This changes all code which feeds CheckResults(sharemap=) to provide
IServer instances, but CheckResults converts these to old-style
serverids during output, so downstream code doesn't have to change yet.

It adds a temporary get_new_sharemap(), which *does* return IServer
instances, so the immutable repairer can build new CheckResults from an
old one. This will go away when get_sharemap() is updated to return
IServer (and downstream code is updated too).