[FEATURE REQUEST] Add Python2 capable agent

[Cx01N]

Is your feature request related to a problem? Please describe.

When migrating Empire from Python 2 to 3, we lost the ability to use Python 2 agents and can only run v3.

Describe the solution you'd like

The ideal solution is to have a single agent that is both Python 2 and 3 compatible.

Describe alternatives you've considered

Two alternative solutions that would also work are 1) have a dedicated python 2 agent that is not compatible with python 3. 2) have a common launcher that calls dedicated python 2 agent code, similar to how the IronPython staging is implemented.

Additional context

One of the libraries to keep in mind that will need to be updated for cross-compatibility is urllib.request. You can patch it in so it is cross-compatible by adding to the launcher.

                launcherBase += """
                if sys.version_info[0] >= 3:
                    import urllib.request as urllib;
                else:
                    import urllib2 as urllib;
                    """

Additional example code is located at dev...python2_agent_v2