title: reactive forms setValidator and updateOn
body: <p>I'm trying to set a validator on a formControl dynamically and can't seem to get the updateOn: "blur" to work properly.  Instead of on blur it seems to be checking on change.  Is there something special I need to do to get this to work on blur instead of on change.</p>
  
  <pre><code>this.form.get("deviceInfo").controls.deviceNumber.setValidators({validators: [Validators.required, this.checkDeviceExists()], updateOn: 'blur'});
  </code></pre>
  
  <p>added the updateValueAndValidity() but still fires on change instead of blur</p>
  
  <pre><code>var deviceInfo = this.form.get("deviceInfo");
  
  deviceInfo.controls.deviceNumber.setValidators({validators: [Validators.required, this.checkDeviceExists()], updateOn: 'blur'});
  deviceInfo.controls.deviceNumber.updateValueAndValidity();
  </code></pre>