bectl: push space-in-name check down into libbe
This check was previously in `create` only, not applying to renames. It
should really be applied at the libbe level, so that we can avoid
writing about this restriction over and over again.
While we're here: `bectl rename` always succeeds, even when it doesn't.
Start returning the error.
Approved by: re (gjb)
Reported By: Christian McDonald <cmcdonald netgate com>
(cherry picked from commit
dadb9c70938c4ae2c260f6af65752c67ac752284)
(cherry picked from commit
227e52a9c0b0be9656757fec47a2648f5619bf67)