common/rc: Enable _format_swapfile to return the swap size

common/rc: Enable _format_swapfile to return the swap size

Once the kernel is free to not map the full swap file during a swapon call,
it can be useful to know the exact size of the swap area created during
_format_swapfile().

To achieve this, it is needed to change other _format_swapfile() callers to drop
the return value if not required, otherwise, it will be printed to stdout making
such tests to fail.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>