Issue/718 default sg rule

[fraugabel]

added alternative test, because the current test only works for the latest versions of the network and compute services, though older versions are not depricated yet

[mbuechse]

Error handling should be improved (don't just swallow exceptions by printing something to stdout), assert statements should not be used in production, and I suppose the code can be made less redundant and more concise.

[mbuechse]

BTW, I noticed that the test script is incredibly noisy when --debug is used. Okay, probably fine. However, logging is not initialized, so the channel is not included in the log line. This should be changed -- please include the following line:

    logging.basicConfig(format='%(levelname)s: %(message)s', level=logging.INFO)

And if --debug is supplied, the following must be done:

    logging.getLogger().setLevel(logging.DEBUG)

Last not least, the output of the script is not usable in any way. What we need is the following:

• for every violation of a requirement: output a message on the ERROR channel
• for every violation of a recommendation: output a message on the WARNING channel
• the return code should be non-zero precisely when an ERROR had been emitted

Every other output should be on the debug or info channel.

[mbuechse]

I massaged it a bit. LGTM -- please check whether it looks good to you, too.