mon: clear pg delta after some period

If we have not pg_map updates, the delta doesn't update, and can get stuck
with the velocity right before activity stopped.  This is confusing, and
can cause incorrect health warnings about in-progress recovery.

To fix this, zero the delta if there is no activity for
'mon delta reset interval' seconds.

Fixes: #5077
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #295 from ceph/wip-5077

Reviewed-by: Joao Luis <joao.luis@inktank.com>
ceph df: fix si units for 'global' stats

si_t expects bytes, but it was being given kilobytes.

Signed-off-by: Mike Kelly <pioto@pioto.org>
(cherry picked from commit 0c2b738d8d07994fee4c73dd076ac9364a64bdb2)
Merge remote-tracking branch 'gh/next'