schedule: priority option

Default to 1000.  Note that beanstalk priority is 2^31, so this
won't mix well with older code scheduling things at the
beanstalk default priority.

Signed-off-by: Sage Weil <sage@inktank.com>
schedule: show priority on -s

Make output a bit nicer too.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #115 from ceph/wip-priority

add priorities to scheduling