Outdated Mongo 2.4 is installed on slave nodes

Outdated `Mongo 2.4` is installed on outdated `ubuntu-build002` `ubuntu-build003` `ubuntu-build-itest001` slave nodes.

They're used as unit/integration testing for `mistral` + `st2` sources during the release process [`st2cd.mistral_release_candidate`](https://github.com/StackStorm/st2cd/blob/master/actions/workflows/mistral_release_candidate.yaml) workflow.