Motivation

When cluster.close() is called, all in-progress HTTP operations should be cancelled.

Changes

• Add pending_sessions_ in the HTTP session manager to ensure that it has a reference to sessions created by it at all stages of their lifetime. Pending operations are the sessions that are currently connecting (i.e. after they have been removed from idle_sessions_ or created and before being added to busy_sessions_)
• Fix issue where the callback was not called in the case of a timeout (dispatch timeout or overall timeout) while a session is connecting.
• In an HTTP session that is connecting, call the connect callback if it is stopped before it has connected.
• Add the couchbase::core::columnar::client_errc error codes to represent errors that are not the result of a client-server interaction. These are the errors that should be exposed in a platform-idiomatic way in the wrappers, not as
  ColumnarErrors - one example is cancellation which happens on the client-side.
• In pending_query_operation replace the use of columnar::errc::generic for cancellations with the new columnar::client_errc::canceled
• When http_session_manager.close() is called, force all the sessions owned by the manager to stop, not just discarding the pointers.
• Fix seg fault when accessing retry_info_ for a pending_query_operation where the session wrapped by it is nullptr (e.g. in the case of a dispatch timeout)
• Add tests for closing the cluster before columnar execute_query has returned & for closing the cluster while rows are being iterated
• Add test for the dispatch timeout with a columnar query

Results

All tests pass