Allow easier setting of artifact dir
Better setup test directory creation/removal
Abstract rm_rf/mkdir_p to MetricFu::Utility
Fix test failures relating to artifact directory missing

see https://travis-ci.org/metricfu/metric_fu/builds/11808630
Refactor RCovGenerator
Merge pull request #144 from bf4/fix-test-failures-artifact-directory-missing

[Fix] test failures relating to artifact directory missing