sdbusplus: use shorter type aliases

The sdbusplus headers provide shortened aliases for many types.
Switch to using them to provide better code clarity and shorter
lines.  Possible replacements are for:
  * bus_t
  * exception_t
  * manager_t
  * match_t
  * message_t
  * object_t
  * slot_t

Change-Id: Ib77ec68be0c5ffd73a8dcc140e22f011191c9de5
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>