swift-ring-builder currently only displays min_part_hours and
not the amount of time remaining before a rebalance can occur.
This information is readily available and has been displayed
as a quality of life improvement.
Additionally, a bug where the time since the last rebalance
was always updated when rebalance was called regardless of
if any partitions were reassigned. This can lead to partitions
being unable to be reassigned as they never age according to
the time since last rebalance.
Change-Id: Ie0e2b5e25140cbac7465f31a26a4998beb3892e9
Closes-Bug: #1526017
1f3304c515