Executor launcher fetches resources as slave user, instead of executor user.

In launcher.cpp, we currently:
-chown the work direcotry
-fetch executor resources
-unpack them if .zip or .tar.gz files (BUG: This needs to be done as the executor user)
-move into work directory
-switch user
-launch executor

This may be a matter of just switching to the executor user earlier, right before the unpacking occurs.

The result of this is that the unpacked files are owned by root and inaccessible by a non-root executor.