shellcheck plugin is picking up target executables

When hadoop-yarn-server-nodemanager is in the build, it generates target/native/target/usr/local/bin/(test-)container-executor. shellcheck picks these up and throws a "hGetContents: invalid argument (invalid byte sequence)" error.

We need some sort of safety to determine if a file is binary or shell code and/or prevent target directories from getting picked up. I suspect the former to be more reliable than the latter since we can't assume maven.