vsh: Allow vshReadlineInit() to be called multiple times

vsh: Allow vshReadlineInit() to be called multiple times

Thing about vshReadlineInit() is - it's called multiple times.
The first time from vshInit(), when @ctl was filled only
partially (most notably, before any argv parsing is done, hence
ctl->imode is set to false). The second time after argv parsing,
from virshInit() -> vshInitReload(). In here, ctl->imode might
have changed and thus vshReadlineInit() can't exit early - it
needs to set up stuff for interactive mode (history basically).

To allow vshReadlineInit() to be called again,
vshReadlineDeinit() must set @autoCompleteOpaque to NULL.

Fixes: cab1e71f0161fd24c5d6ff4c379d3a242ea8c2d9
Resolves: https://issues.redhat.com/browse/RHEL-53560
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>