Give us the ancestor for when the pool had a past value for pg_num.

Signed-off-by: Sage Weil <sage@inktank.com>

Feed in the ancestor pg_t (if any) when we are looking at intervals for
previous maps that may have preceded a recent split.

Fixes: #8139
Signed-off-by: Sage Weil <sage@inktank.com>

In several places, a change in the up_primary triggers a new peering
interval, but the palces that actually generate the new past intervals,
including check_new_interval(), did not enforce that.  This becomes
somewhat obvious when you see that those callers are ignoring the
up_primary output argument for pg_to_up_acting_osds().

Fix this by adding arguments to check_new_interval and fixing the callers
to pass them in properly.  Add a unit test case to verify this.

Note that the past interval struct itself does not record who the
up_primary was; possibly it should.

Fixes: #8139
Signed-off-by: Sage Weil <sage@inktank.com>

Signed-off-by: Sage Weil <sage@inktank.com>

Nothing uses this, but it triggers a new interval, which makes it confusing
when it is not recording in the interval itself.  Let's add it now.

Signed-off-by: Sage Weil <sage@inktank.com>

Also make up vs acting explicit.

Signed-off-by: Sage Weil <sage@inktank.com>