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

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I41103c892db258a85640aa1442acd9a295c8a847
diff --git a/discover_system_state.cpp b/discover_system_state.cpp
index e7f0978..28399bd 100644
--- a/discover_system_state.cpp
+++ b/discover_system_state.cpp
@@ -182,7 +182,7 @@
             }
         }
     }
-    catch (const sdbusplus::exception::exception& e)
+    catch (const sdbusplus::exception_t& e)
     {
         error("Error in PowerRestorePolicy Get: {ERROR}", "ERROR", e);
         elog<InternalFailure>();