Add curl timeout to New Relic API request, to prevent hung php worker / failed deploy workflow

[tinefin]

It would be great to add a timeout to the curl request somewhere around here:
https://github.com/pantheon-systems/quicksilver-examples/blob/master/new_relic_deploy/new_relic_deploy.php#L63L69

As php does not count external processing toward php timeout, it will cause the php worker to hang in case New Relic fails to respond. This will also cause the Deploy workflow to be marked as failed on the site's Dashboard.
http://php.net/manual/en/info.configuration.php#ini.max-execution-time
http://php.net/manual/en/function.set-time-limit.php#refsect1-function.set-time-limit-notes

Internal support ticket reference:
120299