Follow-up from "Fix paraview-config script"

The following discussion from !3939 (merged) should be addressed:

• @dalcinl started a discussion: (+2 comments)

  What was not working with the previous syntax @dalcinl ?

  @mwestphal I have a makefile using paraview-config to get compiler and linker flags to build a Catalyst adaptor. The linker flags had all the VTK stuff, but the ParaView stuff was missing. After inspecting the actual sources, the issue was rather obvious, the ParaView_LIBRARIES variable was misspelled.

  BTW, this new paraview-config script requires a bit more of work, right now is is a bit hard to use. For example, if I run it with no args:

  $ catalyst/bin/paraview-config 
  CMake Error at CMakeLists.txt:5 (find_package):
    By not providing "FindParaView.cmake" in CMAKE_MODULE_PATH this project has
    asked CMake to find a package configuration file provided by "ParaView",
    but CMake did not find one.
  
    Could not find a package configuration file provided by "ParaView" with any
    of the following names:
  
      ParaViewConfig.cmake
      paraview-config.cmake
  
    Add the installation prefix of "ParaView" to CMAKE_PREFIX_PATH or set
    "ParaView_DIR" to a directory containing one of the above files.  If
    "ParaView" provides a separate development package or SDK, be sure it has
    been installed.
  
  
  Traceback (most recent call last):
    File "catalyst/bin/paraview-config", line 254, in <module>
      vtk_components=opts.vtk_components)
    File "catalyst/bin/paraview-config", line 161, in extract_paraview_flags
      stdout=stdout)
    File "/usr/lib64/python3.7/subprocess.py", line 363, in check_call
      raise CalledProcessError(retcode, cmd)
  subprocess.CalledProcessError: Command '['cmake', '-GUnix Makefiles', '/tmp/tmpmfpmutdc/src']' returned non-zero exit status 1.

  There are to obvious issues here:

  1. If running with no cmdline args is not allowed (should it?), this should print help (to stderr) and exit (with error) rather than getting the output above.
  2. The path to paraview-config.cmake should default to the one where the file is installed. This should be easy to implement with CMake's @variable@ substitution. Asking the user to pass the path with -p -p <PARAVIEW-ROOT-DIR>/lib/cmake/paraview-X.Y is cumbersome, you need to know X.Y in advance or implement more hackery like resolving the root dir from the path of the config script.