In the future, this function is going to be called from
vshReadlineParse() to provide parsed input for completer
callbacks. The idea is to allow the callbacks to provide more
specific data. For instance, for the following input:

  virsh # domifaddr --domain fedora --interface <TAB><TAB>

the --interface completer callback is going to be called. Now, it
is more user friendly if the completer offers only those
interfaces found in 'fedora' domain. But in order to do that it
needs to be able to retrieve partially parsed result.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>