tools: Pass opaque data in vshCompleter and introduce autoCompleteOpaque

tools: Pass opaque data in vshCompleter and introduce autoCompleteOpaque

This patch changes the signature of vshCompleters, allowing to pass along
some data that we might want to along with the completers; for example,
we might want to pass the autocomplete vshControl along with the
completer, in case the completer requires a connection to libvirtd.

Signed-off-by: Nishith Shah <nishithshah.2211@gmail.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>