Allow Connection on Different Path (from /gremlin)

Hi

It appears that the Java driver for Gremlin clients only supports connecting to hosts on a fixed path (/gremlin). This is based on the code in tinkerpop/gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Host.java 

The function makeUriFromAddress doesn't provide a method for customizing the path to use. The need arises from proxying multiple server instances through a simple NGINX type proxy where you want to host each one under a different path, currently you would need to use a different hostname or port on the proxy which isn't so desirable. It would seem a relatively simple non breaking change and provides a little bit more flexibility in usage. Other clients like the Python one provide this naturally through passing of the websocket URL.

Thanks

Tony