Enable ntp check by default

[remh]

Also:

• Add a better way to have checks enabled by default
• Fix Stop packaging network.yaml #620
• Ensure that we cast exception as string (otherwise pickle can fail
  when persisting the collector status)

Supersedes #1430

[LeoCavaille]

Looks good to me, will merge once it passed the CI.

[miketheman]

Hi @remh !
(Looking at DataDog/chef-datadog#182) Curious how a file placed on disk with a similar name like conf.d/ntp.yaml with overrides would affect this new behavior - can you comment on how this should work?

[remh]

Hey @miketheman !

If a .yaml file is present, the agent will use this one.
If a .yaml file is not present, the agent will load the .yaml.default

Logic is here:

dd-agent/config.py

Lines 785 to 807 in c7cb52d

	conf_path = os.path.join(confd_path, '%s.yaml' % check_name)
	# Default checks are checks that are enabled by default
	# They read their config from the "[CHECKNAME].yaml.default" file
	if check_name in DEFAULT_CHECKS:
	default_conf_path = os.path.join(confd_path, '%s.yaml.default' % check_name)
	else:
	default_conf_path = None
	conf_exists = False
	if os.path.exists(conf_path):
	conf_exists = True
	elif not conf_exists and default_conf_path is not None:
	if not os.path.exists(default_conf_path):
	log.error("Default configuration file {0} is missing".format(default_conf_path))
	continue
	conf_path = default_conf_path
	conf_exists = True
	if conf_exists:
	f = open(conf_path)

Does that make sense ?

[remh]

So basically this PR DataDog/chef-datadog#182 shouldn't cause any trouble.

[miketheman]

@remh Thanks!