Enable cold benchmarking

[epotyom]

Spin-off from apache/lucene#15458 and discussion with @mikemccand.

luceneutil and nightly benchmarks are all hot. Is there a way to do cold testing? What do people do today for that?

[mikemccand]

I know @rmuir wrote a ramhog.c at one point, which simply ties up X GB of your system's RAM (removes it from consideration by the OS), simulating a box with less RAM.

[rmuir]

Code still compiles and works:

luceneutil/src/python/ramhog.c

Lines 24 to 26 in fc7661f

	/*
	* Hogs the specified amount of memory for benchmarking purposes
	*/