(TK-101) Re-throw IOException from AsyncClose/close call

This commit rethrows any `IOException` caught on a closeable close call
made from the `AsyncClose` class.

src/java/com/puppetlabs/http/client/impl/AsyncClose.java

@@ -30,6 +30,7 @@ public class AsyncClose {
                 this.closeable.close();
             } catch (IOException ioe) {
                 LOGGER.error("Async close error", ioe);
+                throw new RuntimeException("Async close error", ioe);
             }
         }
     }