auto completion for array of values in url parameters

Currently we cannot define autocompletion for url parameters if the parameter can take a list of values such as `h=host,ip,port` .

Once this is fixed we also need to fix kb for `_cat/nodeattrs` , see
https://github.com/elastic/sense/pull/16

Locate the URL-parameter autocomplete code and the knowledge-base entry for `_cat/nodeattrs`; the issue gives the expected list-valued parameter example and points to pull request 16. Done means autocomplete works when a URL parameter accepts comma-separated values and the `_cat/nodeattrs` knowledge base is updated accordingly.

Written by the indexing model from the issue text.