additional check for disk use

This is required while testing on CERN openstack
No, this will not work :

OpenStack (why this error came)
```
['Filesystem           1K-blocks    Used Available Use% Mounted on', 
 '/dev/mapper/VolGroup00-LogVol00',        #FAIL
 '                      70282820 5074640  61640516   8% /', #FAIL
 'tmpfs                  4029724       0   4029724   0% /dev/shm', 
 '/dev/vda1               396672   63209    312983  17% /boot', 
 '/dev/vdb              82569904  188376  78187224   1% /mnt', 
 'AFS                    9000000       0   9000000   0% /afs', '']
```
Fnal machine (did not saw error here)
```
['Filesystem         1K-blocks    Used    Available Use% Mounted on',
 '/dev/sda2           41284928 2581948     36605828   7% /',
 'tmpfs               32975364       0     32975364   0% /dev/shm',
 '/dev/sda1            1032088   62888       916772   7% /boot',
 '/dev/sda5          898472376 3493352    849339192   1% /storage/local/data1',
 'tmpfs                4194304     248      4194056   1% /mnt/ramdisk', 
 'eosprodunmerged 128000000000       0 128000000000   0% /lustre/unmerged', '']
```
Maybe have additional if len(split) == 5 then .... elif len(split) == 6 then ...?