Allow system netcdf

FindNetCDF.cmake adapted from
  https://github.com/jedbrown/cmake-modules/blob/master/FindNetCDF.cmake

Change-Id: I5e790941624e4ab9a37f46687a18a3fd046be6de
Merge topic 'allow-system-netcdf' into master

7f4a0e16 Allow system netcdf