RFR: JDK-8243156 Fix deprecation and unchecked warnings in microbenchmark

[Magnus Ihse Bursie]

This patch addresses the warnings deprecation and unchecked, which are 
impossible to fully suppress.

With this patch, the test-image can be built fully without warnings.

The patch updates non-critical code to use modern solutions for 
deprecated methods, where possible. Tested methods have been annotated 
with SuppressWarnings instead. I'm leaving it for a future update by the 
perf team to reconsider if it's worth testing deprecated methods.

Bug: https://bugs.openjdk.java.net/browse/JDK-8243156
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8243156-fix-warnings-in-microbenchmark/webrev.01

/Magnus