Limit partition movement when adding a new tier

When adding a new tier (region, zone, node, device) to an existing,
already balanced ring all existing partitions in the existing tiers of
the same level are gathered for reassigning, even when there is
not enough space in the new tier. This will create a lot of unnecessary
replication traffic in the backend network.

For example, when only one region exists in the ring and a new region is
added, all existing parts are selected to reassign, even when the new
region has a total weight of 0. Same for zones, nodes and devices.

This patch limits the number of partitions that are choosen to reassign
by checking for devices on other tiers that are asking for more
partitions.

Failed devices are not considered when applying the limit.

Co-Authored By: Florent Flament <florent.flament-ext@cloudwatt.com>
Change-Id: I6178452e47492da4677a8ffe4fb24917b5968cd9
Closes-Bug: 1367826
Merge "Limit partition movement when adding a new tier"