common/types: make numbers a bit nicer when displaying space usage

common/types: make numbers a bit nicer when displaying space usage

Was:
----------------------------------------------------------------------------
GLOBAL:
    SIZE       AVAIL      RAW USED     %RAW USED
    30911M     27050M        3861M         12.49
POOLS:
    NAME                  ID     USED        %USED     MAX AVAIL     OBJECTS
    rbd                   0      101216k      1.10         8913M        1178
    cephfs_data_a         1            0         0         8913M           0
    cephfs_metadata_a     2          892         0         8913M          21
----------------------------------------------------------------------------

Now:
----------------------------------------------------------------------------
GLOBAL:
    SIZE      AVAIL     RAW USED     %RAW USED
    30.2G     26.4G        3.77G         12.50
POOLS:
    NAME                  ID     USED      %USED     MAX AVAIL     OBJECTS
    rbd                   0      99.2M      1.10         8.70G        1180
    cephfs_data_a         1          0         0         8.70G           0
    cephfs_metadata_a     2        892         0         8.70G          21
----------------------------------------------------------------------------

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