vshReadlineParse: Bring some variables into !state block

vshReadlineParse: Bring some variables into !state block

On readline completion vshReadlineCompletion() is called which
does nothing more than calling rl_completion_matches() with
vshReadlineParse() as a callback. This means, that
vshReadlineParse() is called repeatedly, each time returning next
completion candidate, until it returns NULL which is interpreted
as the end of the list of candidates.

The function takes two parameters: @text which is a portion of
input line around cursor when TAB was pressed, and @state. The
@state is an integer that is zero on the very first call and
non-zero on each subsequent call (in fact, readline does @state++
on each call).

Anyway, the idea is that the callback gets the whole list of
candidates on @state == 0 and returns one candidate at each call.
And this is what vshReadlineParse() is doing but some variables
(@partial, @cmd and @opt) are really used only in the @state == 0
case but declared for whole function. We can limit their scope by
declaring them inside the @state == 0 body which also means that
they don't have to be static anymore.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>