Add --es.disable-basic-auth option

[bpot]

This is useful when using Amazon's Elasticsearch service with a VPC
endpoint and ip-based access control.

I also considered automatically skipping the SetBasicAuth option if username and password were empty but it seems nicer to make it explicit.

[coveralls]

Coverage remained the same at 100.0% when pulling 7b7d4c4 on ReturnPath:bp/no_basic_auth into ee916be on jaegertracing:master.

[yurishkuro]

I don't think this is needed. If the username or password are blank, the basic auth will already be disabled. E.g. this is what the olivere's driver does

func SetBasicAuth(username, password string) ClientOptionFunc {
	return func(c *Client) error {
		c.basicAuthUsername = username
		c.basicAuthPassword = password
		c.basicAuth = c.basicAuthUsername != "" || c.basicAuthPassword != ""
		return nil
	}
}

[bpot]

It looks like you're right. I was using docker image 1.0.0 and everything is working with 1.1.0. The problem was probably the lack of ssl certs in 1.0.0 and not basic auth.