PGLog::claim_log_and_clear_rollback_info: fix rollback_info_trimmed_to

We have been setting it to the old head value.  This is usually
harmless since the new head will virtually always be ahead of the
old head for claim_log_and_clear_rollback_info, but can cause trouble
in some edge cases.

Fixes: #9481
Backport: firefly
Signed-off-by: Samuel Just <sam.just@inktank.com>
PG: set info.last_epoch_started on activate even if backfill

If we only find backfill peers, we still want min_last_update_acceptable
to be determined by those backfill peers.  I think this was an oversight
from the acting->actingbackfill switch.

Fixes: #9482
Backport: firefly
Signed-off-by: Samuel Just <sam.just@inktank.com>
PG::find_best_info: let history.last_epoch_started provide a lower bound

If we find a info.history.last_epoch_started above any
info.last_epoch_started, we must be missing updates and
min_last_update_acceptable should provisionally be max().

Fixes: #9482
Backport: firefly
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge remote-tracking branches 'wonzhq/req-pending', 'origin/wip-9326', 'somnathr/wip-optracker-optimization', 'origin/wip-8315', 'upstream/wip-7767-b', 'origin/wip-9453', 'origin/wip-9481' and 'origin/wip-9482' into wip-sam-testing