Recognise a session that is already open to the same bmc

The check for sharing a live session compared the credentials a session
keeps encoded against the strings every caller passes, so it never matched
and each caller built another session beside the one it could not see.
Normalise both sides.  Three commands to one bmc went from three sessions on
three sockets to one, and from five sessions open on the bmc to three.

Not from the port to asyncio: upstream compares the same two things the same
way.

confluent_server/aiohmi/ipmi/private/session.py

@@ -251,6 +251,18 @@ async def _poller(timeout=0):
     return sessionqueue
 
 
+def _credkey(value):
+    """A credential in the form a session keeps it, so callers can be compared
+
+    A session encodes what it was given, while the checks for sharing one are
+    built from whatever the caller passed.  Put both through here.
+    """
+    try:
+        return value.encode('utf-8')
+    except AttributeError:
+        return value
+
+
 def _aespad(data):
     """ipmi demands a certain pad scheme, per table 13-20 AES-CBC encrypted
 
@@ -450,7 +462,7 @@ class Session(object):
                 keepalive=True):
         trueself = None
         forbidsock = []
-        sesskey = (bmc, userid, password, port, kg)
+        sesskey = (bmc, _credkey(userid), _credkey(password), port, kg)
         for res in socket.getaddrinfo(bmc, port, 0, socket.SOCK_DGRAM):
             sockaddr = res[4]
             if ipv6support and res[0] == socket.AF_INET:
@@ -466,8 +478,8 @@ class Session(object):
                         del cls.bmc_handlers[sockaddr][portself[0]]
                         continue
                     if (self.bmc == bmc
-                            and self.userid == userid
-                            and self.password == password
+                            and self.userid == _credkey(userid)
+                            and self.password == _credkey(password)
                             and self.kgo == kg):
                         trueself = self
                         break