pseq: Add presence checking

As a circumvention for hardware problems, it can be necessary to check
for device presence in order to prevent calling out not present
components. Add the ability to configure presence checking in the PSEQ
configuration files and use presence, when configured, in problem
determination.

Signed-off-by: Jim Wright <jlwright@us.ibm.com>
Change-Id: Ia9d8ee57f2d643f61ece45d9c03d523b891e98b8
diff --git a/phosphor-power-sequencer/src/power_control.cpp b/phosphor-power-sequencer/src/power_control.cpp
index eac5ba4..91021a4 100644
--- a/phosphor-power-sequencer/src/power_control.cpp
+++ b/phosphor-power-sequencer/src/power_control.cpp
@@ -84,7 +84,7 @@
                 name = std::get_if<std::string>(&properties[namePropertyName]);
             }
         }
-        catch (std::exception& e)
+        catch (const std::exception&)
         {}
     }
 
@@ -305,7 +305,7 @@
             getDeviceProperties(properties);
         }
     }
-    catch (const std::exception& e)
+    catch (const std::exception&)
     {
         // Interface or property not found. Let the Interfaces Added callback
         // process the information once the interfaces are added to D-Bus.