add after_fork method to HA environment and use it in LRM

add after_fork method to HA environment and use it in LRM

As both the realtime simulator and the real world Environment can
fork but we only need to clean up after a fork in the real world
introduce a after_fork method

In PVE2 it closes the inherited INotify fd and reopens it for the
worker.
Also a cfs_update gets triggered as (other) workers may change the
cluster state.

also use the new introduction HA-Env method to clean up after
we forked an LRM worker.

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