ReplicatedPG::_scrub: account for clone_overlap on each clone

Otherwise, we end up subtracting off clone_overlap for evicted clones
whose sizes we did not add in.

Fixes: #7964
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: use get_clone_bytes on evict/promote

Fixes: #7964
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: do not evict head while clone is being promoted

Fixes: #8003
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG::make_writeable: check for evicted clone before adjusting for clone_overlap

Fixes: #7964
Signed-off-by: Samuel Just <sam.just@inktank.com>