lib.ptree: start manager before setting initial configuration
lib.ptree: start manager before setting initial configuration

We observed a deadlock in the syscall migrate_pages when calling it from
the worker processes concurrently to the manager process.

This seems to avoid this by making sure that the manager process binds
to a NUMA node before forking the worker processes.

The relevant call chain here is:
Manager:start() -> cpuset:bind_to_numa_node() ->
numa.bind_to_numa_node() -> S.migrate_pages(...)

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