crypto: add newline to cert and key if not present

After one of OpenSSL updates we have stopped accepting PEM private keys
and certificates that doesn't end with a newline (`\n`) character.
Handle this regression in `crypto.js` to make less trouble to our users.

fix #6892
node: only run same AL once on error

Should have been included with 60fcc11 as it is the same type of fix.
node: remove asyncStack

Now that the context stores the active execution stack, and because
removeAsyncListener() always removed the AsyncListener from the queue
and the stack, there's no need to keep a stack around anymore. Instead
the active asyncQueue and the currentContext is able to handle it all.