rework __heartbeat__ log message - heartbeat failure is a .warn(), not an...

rework __heartbeat__ log message - heartbeat failure is a .warn(), not an error().  the latter indicates an unexpected condition that should never happen in production.  thought here is that the dependee that's failing should have errors() in her log message, and the depener should have warnings.  Also, this gets error messages out of the console output of the unit test.

lib/heartbeat.js

@@ -52,8 +52,8 @@ exports.setup = function(app, options, cb) {
               ok(false, e);
             }
           } else {
-              logger.error("Not all dependencies are available");
-              ok(false, '\n' + notOk.join('\n') + '\n');
+            logger.warn("heartbeat failed due to dependencies - " + notOk.join(', '));
+            ok(false, '\n' + notOk.join('\n') + '\n');
           }
         }
       };
@@ -104,13 +104,14 @@ var check = exports.check = function(url, cb) {
     clearTimeout(timeoutHandle);
     if (res.statusCode === 200) cb(true);
     else {
-      logger.error("non-200 response from " + shortname + ".  fatal! (" + res.statusCode + ")");
+      logger.warn("heartbeat failure: non-200 response from " + shortname + ".  fatal! (" +
+                  res.statusCode + ")");
       cb(false, "response code " + res.statusCode);
     }
   });
   req.on('error', function (e) {
     clearTimeout(timeoutHandle);
-    logger.error("can't communicate with " + shortname + ".  fatal: " + e);
+    logger.warn("heartbeat failure: can't communicate with " + shortname + ".  fatal: " + e);
     cb(false, e);
   });
 };