osd: throttle snap trimmming with simple delay

This is not particularly smart, but it is *a* knob that lets you make
the snap trimmer slow down.  It's a flow and a simple delay, so it is
adjustable at runtime.  Default is 0 (no change in behavior).

Partial solution for #6278.

Signed-off-by: Sage Weil <sage@inktank.com>
osd/SnapMapper: debug

Signed-off-by: Sage Weil <sage@inktank.com>
osd/SnapMapper: pass snaps set by const ref

Signed-off-by: Sage Weil <sage@inktank.com>
mailmap: Guang Yang name normalization

Signed-off-by: Loic Dachary <loic@dachary.org>
mailmap: Warren Usui name normalization

Signed-off-by: Loic Dachary <loic@dachary.org>
mailmap: Florent Bautista affiliation

and name normalization

Signed-off-by: Loic Dachary <loic@dachary.org>
Revert "ReplicatedPG: block scrub on blocked object contexts"

This reverts commit e66f2e36c06ca00c1147f922d3513f56b122a5c0.
Reviewed-by: Sage Weil <sage@inktank.com>
Merge pull request #1759 from dachary/wip-mailmap

DNM: mailmap updates

Reviewed-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #1694 from ceph/wip-throttle-snap-master

osd: throttle snap trimmming with simple delay

Reviewed-by: Samuel Just <sam.just@inktank.com>
Merge pull request #1698 from ceph/wip-snapmapper-debug

osd/SnapMapper: debug

Reviewed-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: block scrub on blocked object contexts

Fixes: #8011
Signed-off-by: Samuel Just <sam.just@inktank.com>