Allow configurable timeout for DNS lookups.

[atheken]

Investigate options for allowing longer DNS lookup windows.

From user report:

"I looked at the result of the $response request in postmark.../wp-mail.php and got this error:

wp-error - http request error - name lookup timed out.

It appears my dns was a bit slow. So I looked up the docs of the wp_remote_post function and added a timeout option to the $args array and that fixed it."

[mgibbs189]

@atheken The WP_Http library already has hooks to control timeouts. I don't think this warrants its own UI settings since it's an edge case.

E.g. the http_request_args and http_request_timeout filters