Correct information in TESTING.md
Correct information in TESTING.md

* Provide instructions to build the project and execute the unit tests
  in the build
* Remove unneeded flags that disable plugins that execute later in the
  build lifecycle
* Fix markdown underscore
* Add link to Maven lifecycle introduction

milleruntime/accumulo,milleruntime/accumulo,apache/accumulo,ctubbsii/accumulo,phrocker/accumulo-1,mjwall/accumulo,apache/accumulo,apache/accumulo,milleruntime/accumulo,phrocker/accumulo-1,mjwall/accumulo,mjwall/accumulo,milleruntime/accumulo,apache/accumulo,ctubbsii/accumulo,apache/accumulo,milleruntime/accumulo,apache/accumulo,ctubbsii/accumulo,ctubbsii/accumulo,mjwall/accumulo,ctubbsii/accumulo,mjwall/accumulo,phrocker/accumulo-1,ctubbsii/accumulo,ctubbsii/accumulo,phrocker/accumulo-1,mjwall/accumulo,milleruntime/accumulo,phrocker/accumulo-1,phrocker/accumulo-1,mjwall/accumulo,phrocker/accumulo-1,apache/accumulo,milleruntime/accumulo