Description of problem:
When using ssm list, I get a traceback instead of expected result.

Version-Release number of selected component (if applicable):
system-storage-manager-0.2-3.fc20.noarch

How reproducible:
Always

Steps to Reproduce:
1. ssm list


Actual results:

Traceback (most recent call last):
  File "/usr/bin/ssm", line 33, in <module>
    sys.exit(main.main())
  File "/usr/lib/python2.7/site-packages/ssmlib/main.py", line 1485, in main
    args.func(args)
  File "/usr/lib/python2.7/site-packages/ssmlib/main.py", line 966, in list
    self.dev.ptable()
  File "/usr/lib/python2.7/site-packages/ssmlib/main.py", line 700, in dev
    self._dev = Devices(options=self.options)
  File "/usr/lib/python2.7/site-packages/ssmlib/main.py", line 590, in __init__
    my_btrfs = btrfs.BtrfsDev(options=self.options)
  File "/usr/lib/python2.7/site-packages/ssmlib/backends/btrfs.py", line 281, in __init__
    super(BtrfsDev, self).__init__(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/ssmlib/backends/btrfs.py", line 102, in __init__
    fs_used = get_real_number(array[6])
  File "/usr/lib/python2.7/site-packages/ssmlib/backends/btrfs.py", line 36, in get_real_number
    number = float(string[0:-2])
ValueError: invalid literal for float(): 19.08G

Expected results:

Not this.

Additional info: