Fixed improper size displaying in 'df' utility

'df' command used to display filesystem usage statistics as integer
values, in most cases rounding the actual value down. Because of
that 'df' tended to display faulty size values.
This fix to 'df' utility calculates the fractional part of the size,
then it rounds it when needed to the nearest one-digit integer value
and displays after decimal dot.

Change-Id: I9bc52635d45d3e55ce61b3b1c6b80d1267516e75