REST: For enumerate, try GetAll as last resort

If there are no ObjectManager instances covering a
path that came back from the GetSubTree call, the only
other way to get that path's properties is by directly
reading them.

So, after all of the GetManagedObjects calls are done,
on any of the paths that were in the GetSubTree results
but not in the enumerate results, make a GetAll call to
get the properties and add them to the output.

The code knows when all of the asynchronous GetManagedObjects
calls are done because it is called from the destructor of the
InProgressEnumerateData struct which is passed to all of the
other asio ops via a shared pointer.

Tested:  Run on paths that weren't in object managers, such as
         the physical LED objects.

Change-Id: I5a62b9a0ee27a68127e6f216625ce93c9ac58d08
Signed-off-by: Matt Spinler <spinler@us.ibm.com>