Only run 'startup sequence' on reconnect

When a client loses a connection it will currently need to re-subscribe
for symbols and receive a symbol data summary as a first quote response.
Only run the provided coroutine on reconnect and call the kwarg
`on_reconnect`. The client consuming code is entirely expected at this
point to know how the symbol registration protocol works.

piker/brokers/core.py

@@ -116,11 +116,11 @@ class Client:
     """
     def __init__(
         self, sockaddr: tuple,
-        startup_seq: Coroutine,
+        on_reconnect: Coroutine,
         auto_reconnect: bool = True,
     ):
         self.sockaddr = sockaddr
-        self._startup_seq = startup_seq
+        self._recon_seq = on_reconnect
         self._autorecon = auto_reconnect
         self.squeue = None
 
@@ -128,7 +128,6 @@ class Client:
         sockaddr = sockaddr or self.sockaddr
         stream = await trio.open_tcp_stream(*sockaddr, **kwargs)
         self.squeue = StreamQueue(stream)
-        await self._startup_seq(self)
         return stream
 
     async def send(self, item):
@@ -168,6 +167,8 @@ class Client:
                     continue
                 else:
                     log.warn("Stream connection re-established!")
+                    # run any reconnection sequence
+                    await self._recon_seq(self)
                     break
             except (OSError, ConnectionRefusedError):
                 if not down: