ReplicatedPG: do not evict head while clone is being promoted

Fixes: #8003
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge remote-tracking branches 'origin/wip-sam-testing2', 'upstream/wip-7659', 'origin/wip-7904', 'origin/wip-7916', 'origin/wip-7942' and 'origin/wip-7964' into wip-sam-testing