btrfs-progs: mkfs: make the summary more compact

btrfs-progs: mkfs: make the summary more compact

Single device example:

btrfs-progs v4.0.1-39
See http://btrfs.wiki.kernel.org for more information.

Label:              (null)
UUID:               a88bfc85-b454-4a32-8de7-276c01f04d58
Node size:          16384
Sector size:        4096
Filesystem size:    2.00GiB
Block group profiles:
  Data:             single            8.00MiB
  Metadata:         single            8.00MiB
  System:           single            4.00MiB
SSD detected:       no
Incompat features:  extref, skinny-metadata
Number of devices:  1
Devices:
   ID        SIZE  PATH
    1     2.00GiB  /dev/sda

Multiple devices:

btrfs-progs v4.0.1-39
See http://btrfs.wiki.kernel.org for more information.

Label:              (null)
UUID:               9db282ef-55f3-4070-a59f-012a654614b2
Node size:          16384
Sector size:        4096
Filesystem size:    8.00GiB
Block group profiles:
  Data:             RAID6           417.50MiB
  Metadata:         RAID6           417.50MiB
  System:           RAID6            20.00MiB
SSD detected:       no
Incompat features:  extref, raid56, skinny-metadata
Number of devices:  4
Devices:
   ID        SIZE  PATH
    1     2.00GiB  /dev/sda
    2     2.00GiB  /dev/sdb
    3     2.00GiB  /dev/sdc
    4     2.00GiB  /dev/sdd

Signed-off-by: David Sterba <dsterba@suse.cz>