This enables the RestClient to send array-based (multi-valued) header values, rather than only sending whatever happened to be the _last_ value of the header.
Some Rest tests use the Sun HTTP server which has lingering threads after shutdown. Similar to ESTestCase, this adds an
option to wait 5 seconds for these threads to terminate.
:client ---------> :client:rest
:client-sniffer -> :client:sniffer
:client-test ----> :client:test
This lines the client up with how we do things like modules and
plugins.