http2: correct emit error in onConnect, full tests

Correct requestOnConnect to emit session error on
NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE rather than stream error. Add full
test suite for the error handling within requestOnConnect.

PR-URL: https://github.com/nodejs/node/pull/15080
Refs: https://github.com/nodejs/node/issues/14985


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>