storage_vol_page: Use MB in the fields

The fields Swap, Config, Logging and Data are MB.
This patch adds the "MB" in each string for clear understanding
during the process of install ovirt-node.

Change-Id: I0b140ca16ce66237f972acaee3c1bea79c2ff08e
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>