Ensures that the pool default size/min size is set to something
reasonable for a single node (effective RAID-1) and replace teh default
CRUSH replicate_rule set for this situation with one choosing OSD
instead of host as the default.
1. Remove an explicit OSD journal size, especially such a small one (no
clue why I ever added that...)
2. Add max scrubs, disable scrub during recovery, and set scrub sleep.
3. Add max backfills, tune recovery sleep to 0 to prioritize recovery.
Coupled with the removal of explicit --image-features flags to the RBD
command in PVC itself, this ensures that only the two features supported
on kernel 4.19 are enabled by default.