submit plain hostname and fqdn in startup payload

[xcolour]

right now we only submit the fqdn. we should post the regular hostname too so they all can be aliased.

[alq666]

@xcolour how do you want them?

{ 'hostname': 'blah', 'fqdn': 'blah.domain.com'}

[xcolour]

Let's do:

{ 'hostname': 'blah.domain.com', 'shortname': 'blah' }

That way we can stay consistent with the payload from the currently released version of the agent.

[alq666]

Hmm I thought hostname in the agent is the result of socket.gethostname() which will return the short name.

https://github.com/DataDog/dd-agent/blob/master/checks/__init__.py#L236

[alq666]

2.2.25 is on prod.