The `needs_cleanup` flag needs to be set per-module when an exploit
needs an interactive session to clean up. Some `FileDropper` exploits
need additional cleanup to what the mixin provides, but since all
`FileDropper`s already mark themselves as needing cleanup those are not
covered here. A few of these could potentially be refactored to use the
original exploitation method to clean up or to compile the list of
files/commands to clean up ahead of time, but that is out of the scope
of this fix.
William Vu