mgr: 'osd df' by specified class or (crush) name

mgr: 'osd df' by specified class or (crush) name

For large clusters, we use device classes to isolate storage pools.
The existing 'osd df' output turns out to be too nosiy, say, if
you care about only single storage pool with osds possibly spanning over
all hosts.

With this change you are now being able to do 'osd df' by class (or by pool,
if you simply use classes to separate different pools), or by a specified
crush bucket name you are currently interested in, which is much more
convenient.

Some examples:
```
$ bin/ceph osd df tree
ID CLASS WEIGHT  REWEIGHT SIZE   RAW USE DATA    OMAP META  AVAIL   %USE  VAR  PGS STATUS TYPE NAME
-1       0.05878        - 60 GiB 6.4 GiB  23 MiB  0 B 6 GiB  54 GiB 10.60 1.00   -        root default
-3       0.02939        - 30 GiB 3.2 GiB  12 MiB  0 B 3 GiB  27 GiB 10.60 1.00   -            host ceph11
 3   aaa 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  56     up         osd.3
 4   bbb 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  58     up         osd.4
 5   ccc 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  60     up         osd.5
-5       0.02939        - 30 GiB 3.2 GiB  12 MiB  0 B 3 GiB  27 GiB 10.60 1.00   -            host ceph12
 0   aaa 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  50     up         osd.0
 1   bbb 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  61     up         osd.1
 2   ccc 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  51     up         osd.2
                    TOTAL 60 GiB 6.4 GiB  23 MiB  0 B 6 GiB  54 GiB 10.60
MIN/MAX VAR: 1.00/1.00  STDDEV: 0

$ bin/ceph osd df tree class aaa
ID CLASS WEIGHT  REWEIGHT SIZE   RAW USE DATA    OMAP META  AVAIL   %USE  VAR  PGS STATUS TYPE NAME
-1       0.05878        - 20 GiB 2.1 GiB 7.8 MiB  0 B 2 GiB  18 GiB 10.60 1.00   -        root default
-3       0.02939        - 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00   -            host ceph11
 3   aaa 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  56     up         osd.3
-5       0.02939        - 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00   -            host ceph12
 0   aaa 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  50     up         osd.0
                    TOTAL 20 GiB 2.1 GiB 7.8 MiB  0 B 2 GiB  18 GiB 10.60
MIN/MAX VAR: 1.00/1.00  STDDEV: 0

$ bin/ceph osd df tree name ceph11
ID CLASS WEIGHT  REWEIGHT SIZE   RAW USE DATA    OMAP META  AVAIL   %USE  VAR  PGS STATUS TYPE NAME
-3       0.02939        - 30 GiB 3.2 GiB  12 MiB  0 B 3 GiB  27 GiB 10.60 1.00   -            host ceph11
 3   aaa 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  56     up         osd.3
 4   bbb 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  58     up         osd.4
 5   ccc 0.00980  1.00000 10 GiB 1.1 GiB 3.9 MiB  0 B 1 GiB 9.0 GiB 10.60 1.00  60     up         osd.5
                    TOTAL 30 GiB 3.2 GiB  12 MiB  0 B 3 GiB  27 GiB 10.60
MIN/MAX VAR: 1.00/1.00  STDDEV: 0

```

Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>