'Calculate available space on the share.
:param share: example 172.18.194.100:/var/fs'

def _get_available_capacity(self, share):

    mount_point = self._get_mount_point_for_share(share)
    (out, _) = self._execute('df', '--portability', '--block-size', '1', mount_point, run_as_root=self._execute_as_root)
    out = out.splitlines()[1]
    size = int(out.split()[1])
    available = int(out.split()[3])
    return (available, size)
