Ten definitions name each access by id; the path stays as the default an assignment may replace,
and the host side of every mount says ${access:<id>}. Resolved with no placement, every definition
names exactly the paths it named before (TestPlacedDirectoriesKeepTheirPaths, extended). On an
adopted machine the assignment now says `accesses: {<id>: <path>}` and the mount follows.
Needs the controller that knows an access id (mesh-controller #176); the running one refuses the
field at registration.
jschoubben
684b9853ad