Fix NMS-6356 graph for mib2 storage usage does not work
- Removed CDEF:ceil=100 cause its not valid in RRDtool, but is valid in
  JRobin
- Replaced CEIL with HRULE which is a valid RRDtool definition and is
  not implemented in JRobin see NMS-2793 and will just be ignored
- Maskerade ":" for RRDtool with "\\:"