Use 'order-by' on PuppetDB API queries.

Specify an order for the resources, ensures resources follow a
constant order on the generated files. With this, we can easily
compare (diff, md5) results from several runs.
Added confreplacer.py.

Generates configuration in a temporary directory. Reloads if the new
configuration is ok, rollbacks otherwise.
Removed get_all_config(). Multiple resources can be generated with -r.

The parameter '--resources' accepts a list of comma-separated resource
names.
Config generation moved to a class to improve modularity.
New method write() creates one file for every resource type.

Added option --base-dir. write() creates files inside $base_dir/tmp.d/
Fix: reload functionality had been accidentally removed.
Removed external dependency: path.py
Rollback config if syntax check fails. Every resource in a config file.

A syntax check is run before reloading the configuration. If the check
fails, we rollback to the previous Nagios configuration and abort
reloading. Running repeatedly the script won't break your configuration.

For every requested resource, a configuration file is created in
${base-dir}/tmp.d/. If everything is ok, this configuration will be
moved to ${base-dir}/naginator.d/. Otherwise, you keep your old
configuration and the tmp.d/ dir.
Remove the --stdout option (not needed anymore).
Remove old tests.
New option --tag: return only resources with this tag.
Flake8 mostly everything but some 80 char lines.