Provide a means to initialize GLOG for the executor driver.

Currently we don't initialize google logging from the executor driver, but we do in the scheduler driver.

Scheduler Driver: https://github.com/apache/mesos/blob/0.19.1/src/sched/sched.cpp#L1093
Executor Driver (left as a TODO): https://github.com/apache/mesos/blob/0.19.1/src/exec/exec.cpp#L595

This means that we don't have stacktraces available and it makes it hard to debug mysterious process exits.