Make the generation of random hills consistent across all platforms.

This is done by using the class vtkMinimalStandardRandomSequence to generate
 a random sequence instead of the native random number generators.

There has also been more code cleanup.


Change-Id: I090c21faeee5c9779cc54da1bac4e43c268205c3
Signed-off-by: Andrew Maclean <andrew.amaclean@gmail.com>
Merge topic 'random_hills_use_standard_rng' into master

b898432e Make the generation of random hills consistent across all platforms.