MINIFICPP-439 Prefer cmake3 command when available before using cmake.
MINIFICPP-439 Prefer cmake3 command when available before using cmake.

This closes #287.

Signed-off-by: Aldrin Piri <8746015474cd01110181ed51735247560fd08de4@apache.org>

achristianson/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,benqiu2016/nifi-minifi-cpp,apiri/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,apiri/nifi-minifi-cpp,apiri/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,apiri/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,benqiu2016/nifi-minifi-cpp,benqiu2016/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,apiri/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp