Trigger rubber:config after deploy:update_code

Also added logic to skip `rubber:config` and `deploy:assets:precompile`
during db role bootstrapping.

This commit doesn't break normal deploys (including `deploy:migrations`
or `deploy:migrate`) with a deploy.rb file from old vulcanizations but
boostrap_db may fail if the assets task requires a database connection.
Re-vulcanizing to replace it with the new deploy.rb will fix it.

This will solve issue #258