Reduced Surefire concurrency
Reduced Surefire concurrency

Between Surefire concurrent tests, JaCoCo and Derby; tests were failing
with terminated forked JVMs on Travis CI.
Resolving this by reducing Surefire concurrency to 2 forks (no reuse) /
2 threads.

Change-Id: I6cf18dd1322d4f4650ada9fdbf933aa5e7dd254f

bindul/junit-helper,deventropy/junit-helper