Improve JIT performance for Configuration parsing

In investigating a performance regression for small tasks between Hadoop 2 and Hadoop 3, we found that the amount of time spent in JIT was significantly higher. Using jitwatch we were able to determine that, due to a combination of switching from DOM to SAX style parsing and just having more configuration key/value pairs, Configuration.loadResource is now getting compiled with the C2 compiler and taking quite some time. Breaking that very large function up into several smaller ones and eliminating some redundant bits of code improves the JIT performance measurably.