Revert "Add some crowbar client nodes to /etc/hosts"

This reverts commit 0bc2a9eaef253708c20a6c6fedf237321c5f3100.

DNS aliases seem to be the better solution, check the discussion around
https://github.com/saschpe/automation/commit/0bc2a9eaef253708c20a6c6fedf237321c5f3100