Notifier does not work for Composite build configurations

[hwcc]

Repro:

1. create a project with a few sub-projects
2. create a composite build config under the main project level. Set all the sub projects as dependencies to the composite build config
3. set up slack notification on the build config level to notify when build successful or failed
4. run the build config

expected result:
Slack should have notification for the composite build config for successful or failed builds

actual result:
nothing is posted in Slack

[fatso83]

This would be really useful.