Add hostname to elastalert_status

[Qmando]

If multiple instances are writing documents to elastalert_status, there needs to be some way to determine which machine they came from. Hostname would be useful to have in these logs.

[pdscopes]

I like this idea too. However, I think there should be an optional name property in the config file which defaults to hostname if not set. This would allow users to potentially have multiple instances of EA running on the same host.