osd/scrub: modify (deep)scrub ASOK commands

osd/scrub: modify (deep)scrub ASOK commands

Fix all instances of 'deep_scrub' to the documented format (deep-scrub);

Make all formats of the documented command ('ceph tell $pg
[deep-]scrub', and the old 'ceph pg scrub $pgid') trigger an
operator-priority scrub;

Introduce a dev/tests-only format for the required functionality
of "trigger a scrub by modifying the timestamps".

Change some implementation details.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>