cleanup manager status on start

cleanup manager status on start

Cleanup the manager state in a general way if we get promoted to
manager. This safes us code as instead of having to check all
deprecated entries and delete them, each one extra, we just safe the
state part needed to change master without loosing any result of the
manager status and just delete the rest.
This would include the following keys:
* service status: as it may contain unprocessed results
* manager_node: this is set only once before this cleanup so do not
  delete it.

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>