If some dynamic libraries that agent depends on are stored in a non standard location, and the operator starts the agent using LD_LIBRARY_PATH. When we actually fork/exec the 'mesos-containerizer launch' helper, we need to make sure it inherits agent's environment variables. Otherwise, it might throw linking errors. This makes sense because it's a Mesos controlled process.
However, the the helper actually fork/exec the user container (or executor), we need to make sure to strip the agent environment variables.
The tricky case is for default executor and command executor. These two are controlled by Mesos as well, we also want them to have agent environment variables. We need to somehow distinguish this from custom executor case.