Fixed all volume group run

Howdy,

Fixed the handling for "all" volume groups.
Added in handling for UNKNOWN status and exiting with a fair error message in that case.


Later.
Function volumeGroupExists will check only one vg. 
Multiple vg should be checked by looping over all of them:
https://github.com/veverjak/check_vg_size/blob/master/check_vg_size#L212

Latest fix should fix problem in case that vg name includes empty space. 
If fction volumeGroupExists is called with multiple vgs, its a bug and I should fix it.