MINIFICPP-481: Update agent to exit gracefully with an invalid *repo dir
MINIFICPP-481: Update agent to exit gracefully with an invalid *repo dir

This closes #319

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

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