Java System Properties not documented

[dlmarion]

Accumulo allows the user to modify the behavior of the runtime via Java System properties, but these are not documented anywhere. I found the following:

In CompressionAlgorithm.java, introduced into 2.1.0 via #2518 , the code allows the user to specify a different class name for the different compression algorithms. The value passed in for the property name is the value specified by the getCodecClassNameProperty method in the subclasses of CompressionAlgorithmConfiguration. For example, in 2.1 these are currently io.compression.codec.bzip2.class, io.compression.codec.lz4.class, io.compression.codec.lzo.class, io.compression.codec.snappy.class, and io.compression.codec.zstd.class.

accumulo/core/src/main/java/org/apache/accumulo/core/file/rfile/bcfile/CompressionAlgorithm.java

Lines 292 to 294 in 3ec800b

	if (codecClazzProp != null) {
	clazz = System.getProperty(codecClazzProp, getConf().get(codecClazzProp, defaultClazz));
	}

Other system properties are being used in SiteConfiguration and one is being introduced into 3.1 via #4880.