webadmin: storage disks subtab - fix status column

Storage > Disks:
'Status' column should be fetched using 'getStatusColumn' method.

Change-Id: Ia373c40f696ce080dbfd09252fc96a5b59b3a80c
Bug-Url: https://bugzilla.redhat.com/1133265
Signed-off-by: Daniel Erez <derez@redhat.com>