release start: Assign bugs as well

The candidates for the next release were chosen only from the features
currently available, leaving bugs behind. Since bugs are, however,
treated in the same way as features in the plugin, this was a wrong
behavior.

Change-Id: Id9b4ca3c5e5e15911c1e0964839bfc6e9698e1ab
Signed-off-by: Ondrej Kupka <ondra.cap@gmail.com>