folly/io/async/tests: always detach event base in tests, fixes UBSAN tests

folly/io/async/tests: always detach event base in tests, fixes UBSAN tests

Summary:
In AsyncSSLSocket tests the shared_ptr structure means that the
AsyncSSLSocket-s outlive the stack-allocated EventBase on which they were
created.  Previously there were scattered calls to detachEventBase on the
last interesting callback, but several calls were missing.  This diff
switches to a model where the SSLServerAcceptCallbackBase is responsible
for detaching the sockets.

This diff also fixes a low-firing race between shutdown
of the TestSSLAsyncCacheServer Main thread and a call to
EmptyReadCallback::readEOF.  Most uses of EmptyReadCallback don't attach
the TCP socket, so they can't actually tolerate a call to readError
or readEOF.

These use-after-destruction problems were discovered by UBSAN.

Reviewed By: djwatson

Differential Revision: D4301416

fbshipit-source-id: 127fb5e506d0694c5ca81d7a38c704d69f4ab3eb