Show entitlement jar path in agent load failure

When the entitelement agent fails to load the underlying exception can
be cryptic. In some casees it may be that the path the agent jar is bad.
This commit expands the exception message to show the agent path
that we tried to load.

Author: rjernst

libs/entitlement/src/main/java/org/elasticsearch/entitlement/bootstrap/EntitlementBootstrap.java

@@ -122,7 +122,7 @@ static void loadAgent(String agentPath, String entitlementInitializationClassNam
                 vm.detach();
             }
         } catch (AttachNotSupportedException | IOException | AgentLoadException | AgentInitializationException e) {
-            throw new IllegalStateException("Unable to attach entitlement agent", e);
+            throw new IllegalStateException("Unable to attach entitlement agent [" + agentPath + "]", e);
         }
     }