jcs:open() extension function support for routing-instances

The jcs:open() extension function returns a connection handle that is used to execute RPCs on a local or remote device. To redirect the SSH connection to originate from within a specific routing instance, include the name of the routing instance in the connection parameters. The routing instance must be configured at the [edit routing-instances] hierarchy level, and the remote device must be reachable either using the routing table for that routing instance or from one of the interfaces configured under that routing instance.