fixing incorrect error message when vol parameter is missing

very minor but important error message correction imo , if the config parameter ```"fs.glusterfs.volume.fuse.gv0"``` is missing, then the current error message sais ```"could not find property ~~"fs.glusterfs.fuse.gv0"~~```, which can lead to possible brain explosion :)  It should be ```fs.glusterfs.VOLUME.fuse```.