Cache service names for paths and interfaces

To lookup a service name for a given path and interface, use GetSubTree
to retrieve all the service names from the root path for the interface
and add each entry to a cached dataset.

Tested:
    Check that a missing interface's service is added
    Check that a missing path that exists has its service added
    Inspect all missing paths for an interface are added
    Inspect missing interfaces are added to existing service
    Returned service name matches the service for a path/interface

Change-Id: I6db05479e825350198896b2e237882f7ebc58d51
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
2 files changed