qcreset.set_data_empty crashes for non-shared data

[bkhegstad]

Tested this on a project but it crashed when it tried to empty a non-shared 3D parameter. (Used "all" so it crashed when it came to that parameter)
Potential solutions:
-- Do not crash - only give a warning
-- Delete all realizations
-- Realization(s) can/must be specified

Traceback (most recent call last):
  Python script, line 26
  Python script, line 22, in reset
  File "/project/res/roxapi/x86_64_RH_7/11.1/lib/python3.6/site-packages/fmu/tools/rms/qcreset.py", line 365, in set_data_empty
    prop.set_empty()
ValueError: Realisation must be specified for non-shared data.