Revert "stack/erp5: stop using caucase managed certificate for balancer"

This reverts commit 620c9332 and add a
caucase service for balancer in the balancer partition. The caucase
service from the root partition (that was not used) is remvoed.

TODO:
 - fix json (undo a change)
 - test external caucase in test_erp5
 - test switching from internal caucase to external caucase