Use lastnpe.org stuff to help avoiding the infamous NullPointerException in OpenDaylight code

This is an umbrella / parent issue for me to link http://www.lastnpe.org related work to.

For example https://git.opendaylight.org/gerrit/#/c/47370/ et al.

This work is NOT limited to Eclipse IDE users, but very much includes as a goal to have the CLI mvn build pick up on possible NPE violations as well (and therefore e.g. fail Gerrits introducing regressions). Users of the Eclipse IDE however may get such violations reported while coding, for their convenience.

PS: This is to be seen as complementary to similar static code analysis for NPE offer e.g. by IDEA - but there in the IDE only, for one off looks by interested developers and occasional sporadic fixes; not build enforced such as this will be.

Just like our Checkstyle, FindBugs (and maybe error-prone some day) support offered to all ODL projects by odlparent, I'm anticipating this will be very much of an "opt in" kinda thing.