rpc_client: retry open on STATUS_PIPE_NOT_AVAILABLE

rpc_client: retry open on STATUS_PIPE_NOT_AVAILABLE

Windows Server starts some named pipe services on demand, and responds
to initial open requests with STATUS_PIPE_NOT_AVAILABLE. The FssagentRpc
named pipe on Windows Server 2012 exhibits this behaviour.

This change sees rpcclient retry named pipe open requests when the
server responds with STATUS_PIPE_NOT_AVAILABLE. The retry logic is
contained in an asynchronous tevent_timer callback, to allow for
non-blocking callers.

Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>