Simplify may_write()

CEPH_MDS_OP_CREATE has CEPH_MDS_OP_WRITE bit set so already checked

Signed-off-by: David Zafman <david.zafman@inktank.com>
osd: data loss: low space handling

First building version

Feature: #4197

Signed-off-by: David Zafman <david.zafman@inktank.com>
Move check_failsafe_full() for later change
Fix log message output
Use clock to track warning messages
Use osd_op_complaint_time as time between messages
Use get functions to retrieve failsafe % of nearfull and full

Signed-off-by: David Zafman <david.zafman@inktank.com>