Fixes mode argument with --mode=genanswers

When `sudo atomic run projectatomic/helloapache --mode=genanswers` is
supplied, the resulting error shows that `--mode=genanswers` is an
unrecognized argument.

This was introduced after refactoring the cli/main.py code to NOT include
uneeded parameters such as --provider-auth to CLI options such as init
and genanswers.

By adding `self.parser.parse_known_args`, this will ignore the added
--mode=genaswers to the CLI.

Fixes #792

atomicapp/cli/main.py

@@ -483,7 +483,7 @@ def run(self):
         cmdline.insert(0, args.action)  # Place 'action' at front
 
         # Finally, parse args and give error if necessary
-        args = self.parser.parse_args(cmdline)
+        args, unknown = self.parser.parse_known_args(cmdline)
 
         # Setup logging (now with arguments from cmdline) and log a few msgs
         Logging.setup_logging(args.verbose, args.quiet, args.logtype)