test: flaky test-http-client-parser-double-free

There were two issues that were causing this test to fail
intermittently in release builds:

1. Since the client is only processing one readable event,
   the client request is not enough to keep the process alive
   and the process can exit before the desired events have
   been raised.
2. Reading just 1 byte is not enough to guarantee that the
   parser will eventually consume all the data and raise the
   desired parse error. I tried postponing the server.close()
   to address the issue at [1], but then the test just hangs
   sometimes.