Build and upload wrappers from least busy fallback.

Least busy fallback is determined by memory usage %.  All this is
done on prompt from the controller and the controller is informed
when we're done.  I think this concludes the lantern_aws part of
Merge branch 'issue1265' of github.com:getlantern/lantern_aws into issue1265

Conflicts:
	salt/fallback_proxy/init.sls
	salt/fallback_proxy/report_completion.py