juise should set context variables correctly

[philshafer]

>2.  Is there not a way to access the predefined $product or $hostname param=
>eters like we can when using slax on-box?

The junos-context is set, but mostly empty.  "host-name", "product", "localtime",
"localtime-iso", and "script-type" are there; product is "juise":

<op-script-input xmlns:junos="http://xml.juniper.net/junos/*/junos">
  <junos-context>
    <host-name>bock.juniper.net</host-name>
    <product>juise</product>
    <localtime>Wed May 27 08:34:15 2015</localtime>
    <localtime-iso>2015-05-27 08:34:15 EDT</localtime-iso>
    <script-type>op</script-type>
    <user-context>
      <user>phil</user>
      <uid>501</uid>
      <op-context/>
      <arguments>
        <argument>/Users/phil/work/root/bin/juise</argument>
        <argument>-d</argument>
        <argument>/Users/phil/trash/topology-ospf.slax</argument>
      </arguments>
    </user-context>
  </junos-context>
</op-script-input>

Looks like I'm missing the plumbing to pull this into the script.  juise
should do this automatically, but you can fake it using:

var $junos-context = /op-script-input/junos-context;
var $host-name = $junos-context/host-name;
var $product = $junos-context/product;