Node power sync is performed from a periodic task. In that task
all nodes are iterated over and power sync call is performed.
While the power sync call itself if non-blocking relative to
other concurrent I/O tasks, iteration over the nodes seems
sequential meaning that nodes power sync is performed one node
at a time.
If the above observation holds, large-scale settings may never
be able to power sync all their nodes properly, throttling at
walking all active the nodes in 60 second period.
This patch distributes power sync calls over a bunch of green
threads each working on a portion of the nodes to be taken care
of.
Change-Id: I80297c877d9a87d3bd8fc30d0ed65cd443f200b3