server: We shouldn't exit the server in lazy init. (#2548)

Avoid fatalIf instead these are non-critical errors,
continue running the server.

 - initializing bucket notifications
 - initializing bucket policies.
 - migrating bucket policies failure.

Fixes #2547

cmd/bucket-policy.go

@@ -100,10 +100,13 @@ func initBucketPolicies(objAPI ObjectLayer) error {
 		return err
 	}
 
+	// Populate global bucket collection.
 	globalBucketPolicies = &bucketPolicies{
 		rwMutex:             &sync.RWMutex{},
 		bucketPolicyConfigs: policies,
 	}
+
+	// Success.
 	return nil
 }