Elasticsearch version: 5.x

Plugins installed: []

JVM version:

OS version:

Describe the feature:
In the 5.x reindex api, support for remote is added, e.g,
POST _reindex
{
"source": {
"remote": {
"host": "http://otherhost:9200",
"username": "user",
"password": "pass"
},
...

However the host property is strictly enforced to three parts, scheme, host and port. We host elasticsearch behind a proxy and need the ability to specify a path too. I found code in https://github.com/elastic/elasticsearch/blob/v5.2.0/modules/reindex/src/main/java/org/elasticsearch/index/reindex/RestReindexAction.java, that enforces this rule.

...
private static final Pattern HOST_PATTERN = Pattern.compile("(?[^:]+)://(?[^:]+):(?\d+)");
...

Can we add the support for path?