Team Calendars silently fails to load on startup due to workbox being disabled.

Summary

When workbox is disabled Team Calendars will silently fail.

Steps to Reproduce (In the case of cloud workbox was already disabled after the last system restart but the following steps will reproduce the vague errors. No indication as to why workbox was suddenly disabled)

1. Install the Team Calendars add-on
2. Disable Team Calendars add-on
3. Disable workbox add-on.
4. Enable Team calendars.

Expected Results

Team Calendars would not silently fail with a vague log error that indicates a time out in the UI.

Actual Results

The below exception is thrown in the xxxxxxx.log file:

@40000000575667192d7e2034 2016-06-07 01:17:51,762 INFO [LandlordServiceAcceptTenantThread] [atlassian.plugin.manager.DefaultPluginManager] broadcastPluginDisabling Disabling com.atlassian.confluence.extra.team-calendars
@400000005756683500f8505c 2016-06-07 01:22:35,016 http-nio-127.127.127.127-12998-exec-2 WARN anonymous 82x21x1 - 127.127.127.127 /instantupgrade [c.a.upm.mac.HostLicenseUpdatedHandlerImpl] UPM-5043 Detected a plugin which is licensed but not installed: com.atlassian.confluence.extra.team-calendar

Notes

On startup you get something a little more conclusive if Workbox is disabled but still pretty vague:

@40000000575667170c5dd32c 2016-06-07 01:17:49,206 ERROR [Spring DM Context Creation Timer] [plugin.osgi.factory.OsgiPlugin] logAndClearOustandingDependencies Plugin 'com.atlassian.confluence.plugins.confluence-mobile-rest' never resolved service '&notificationService' with filter '(objectClass=com.atlassian.mywork.service.LocalNotificationService)'
@40000000575667192da1d8bc 2016-06-07 01:17:51,764 ERROR [LandlordServiceAcceptTenantThread] [plugin.osgi.factory.OsgiPlugin] logAndClearOustandingDependencies Plugin 'com.atlassian.confluence.extra.team-calendars' never resolved service '&notificationService' with filter '(objectClass=com.atlassian.mywork.service.NotificationService)'
@40000000575667bd2fd5cfbc 2016-06-07 01:20:35,801 ERROR [UpmScheduler:thread-2] [plugin.osgi.factory.OsgiPlugin] logAndClearOustandingDependencies Plugin 'com.atlassian.confluence.extra.team-calendars' never resolved service '&notificationService' with filter '(objectClass=com.atlassian.mywork.service.NotificationService)'

We should handle this more gracefully. If Workbox is required for Team Calendars it should be auto enabled when Team Calendars is enabled. Also we should improve the logging to be more specific if workbox didn't load instead of giving a timeout failure in the UI.

Workaround

Enable Workbox add-ons via Manage Add-ons (System add-ons)

Then enable Team Calendars.