When running a MR swift deploy we rebalance the ring in quick
succession.
To do this successfully we need to set the
"swift_pretend_min_part_hours_passed" to True. This shouldn't be needed
in a regular deploy, or a deploy where rings don't change.
Change-Id: Ib86dcfbdb5f6346e2c7da67b6bf2b29c62f99dab