Disable test alert button if endpoint is disabled at construction

ui/src/kapacitor/components/AlertTabs.js

@@ -196,6 +196,7 @@ class AlertTabs extends Component {
             onSave={this.handleSaveConfig('slack')}
             config={this.getSection(configSections, 'slack')}
             onTest={this.handleTestConfig('slack')}
+            enabled={this.getEnabled(configSections, 'slack')}
           />,
       },
       smtp: {

ui/src/kapacitor/components/config/SlackConfig.js

@@ -6,8 +6,7 @@ class SlackConfig extends Component {
   constructor(props) {
     super(props)
     this.state = {
-      // if enabled true, else false.
-      testEnabled: true,
+      testEnabled: this.props.enabled,
     }
   }
 
@@ -101,6 +100,7 @@ SlackConfig.propTypes = {
   }).isRequired,
   onSave: func.isRequired,
   onTest: func,
+  enabled: bool.isRequired,
 }
 
 export default SlackConfig