When reopening an issue the Mattermost Notification has no context to the issue

Summary

If you set up Mattermost notifications integration, it correctly sends notifications on opening / closing of issues, however, if you reopen an issue the notifiaction that is sent does not have any context to the issue.

Note: There may be similar issues with notifications sent to other integrations (e.g. Slack) or types of notifications (e.g. Reopening a Merge Request)

Steps to reproduce

1. Set up Mattermost Notification Integration to send notifications on issues to a channel.
2. Create Issue
3. Close Issue
4. Reopen Issue

What is the current bug behavior?

• Current notification indicates an issue was opened, which technically is incorrect as an issue was reopened.
• No context is provided within the notification message as to what issue caused the notification

What is the expected correct behavior?

There should likely be some context to indicate that an issue was reopened and possibly send a preview of the issue within the notifciation

Relevant logs and/or screenshots

Results of GitLab environment info

GitLab EE 10.0.4

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)