changed pom.xml for executing unit tests in parallel
Support maven-findbugs-plugin

FindBugs is a static analyser to look for bugs in Java code.
This change enable mspgack-java to analyse potential bugs by
using FindBugs.

To use findbugs, please type

    $ mvn findbugs:findbugs

Signed-off-by: Tsuyoshi Ozawa <ozawa.tsuyoshi@gmail.com>
Merge branch 'master' of github.com:msgpack/msgpack-java
Merge branch 'findbugs' of github.com:msgpack/msgpack-java