mon/OSDMonitor: list osd tree in named bucket

[kungf]

easy to get osd status in named bucket.
eg.
"ceph osd tree-ls node-1" will only show osds in bucket node-1,

Signed-off-by: kungf yang.wang@easystack.cn
@yangdongsheng

[hjwsm1989]

roots is empty if the bucket doesn't exist?

[kungf]

@hjwsm1989 yes, nothing to show

[xiexingguo]

Seems by accident you changed the mode of this file to be executable ...

[kungf]

thanks, i change it to default

[kungf]

@liewegas need a review, please

[liewegas]

Don't we already have 'ceph osd ls-tree ' that does exactly this? (There is also 'ceph osd crush ls ' that returns the immediate child items.)

[kungf]

@liewegas ceph osd ls-tree only return osd id not with their status and weight, and ceph osd crush ls only return the the direct child items(children may also be bucket ). they don't show the osd status(up, down).
this pr cmd can do:

1. show all osds in one bucket with status, the bucket can be host, rack, row, root ... ,
2. can only show wanted status osds(like ceph osd tree up/down/destory),

[liewegas]

what about s/tree-ls/tree-under/ or tree-from? (The ls-tree vs tree-ls bugs me, and in the other cases 'ls' is always a raw list, not a table.)

[kungf]

@liewegas it's also hard for me to choose a proper command name .
what about tree-in? tree-under is a little long, tree-in may be easier to knock the keyboard

[kungf]

@liewegas cmd name was changed to tree-under, need a review, please

[liewegas]

looks good!

[yuriw]

wip-yuri4-testing-2018-01-02-1711