Add utils module
Add utils module

The first utility is a class that uses the mapper to wait for a
list of dbus objects to appear on the bus.

The wait utility is non-blocking; a callback must be provided.

Change-Id: I12813b32df90090507c461f03d8c54bb71a7c332
Signed-off-by: Brad Bishop <713d098c0be4c8fd2bf36a94cd08699466677ecd@fuzziesquirrel.com>

openbmc/phosphor-objmgr,bradbishop/phosphor-objmgr,openbmc/phosphor-objmgr,bradbishop/phosphor-objmgr,bradbishop/phosphor-objmgr