bin/test_nginx.sh: clean the /etc/nginx dir completely
- rename the prepare_test_show_highstate_env.sh script to
prepare_test_highstate_env.sh as it is used not only for show_highstate
any more, but for various other highstate related tests
- add flag to prepare_test_highstate_env to install extra packages
needed for testing
- install the nginx package, take backup of the /etc/nginx dir and then
reset it before running the nginx tests