Add support for getting all node options via --dump-options flag

This implements gathering information about of all hived options, by using a new command-line option --dump-options, which fixes issue hive#345. A test in hive!724 (closed) requires this to be merged.

Additionally, this feature can be used to reimplement node_config.py. For now, it seems that when a new option is added to hived, node_config.py has to be manually changed to reflect it. After this change it will be possible to parse information regarding all available hived options at runtime.