tls: fix leak of WriteWrap+TLSWrap combination

Writing data to TLSWrap instance during handshake will result in it
being queued in `write_item_queue_`. This queue won't get cleared up
until the end of the handshake.

Technically, it gets cleared on `~TLSWrap` invocation, however this
won't ever happen because every `WriteWrap` holds a reference to the
`TLSWrap` through JS object, meaning that they are doomed to be alive
for eternity.

To breach this dreadful contract a knight shall embark from the
`close` function to kill the dragon of memory leak with his magic
spear of `destroySSL`.

`destroySSL` cleans up `write_item_queue_` and frees `SSL` structure,
both are good for memory usage.

PR-URL: https://github.com/nodejs/node/pull/9586


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>