Avoid unnecessary exception wrapping in JPAConfig

1. To preserve the type of the exception, since we react differently to
   ConfigurationException for example.
2. To make testing cleaner.

extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/JPAConfig.java

@@ -75,7 +75,8 @@ public void run() {
             } catch (InterruptedException e) {
                 throw new RuntimeException(e);
             } catch (ExecutionException e) {
-                throw new RuntimeException(e.getCause());
+                throw e.getCause() instanceof RuntimeException ? (RuntimeException) e.getCause()
+                        : new RuntimeException(e.getCause());
             }
         }
     }