Retry OEM lookup if no specific OEM identified

Some devices might experience a problem returning a useful response to
get device id under certain circumstance.  Make failures due to
inability to lock into a device id transient rather than persistent.

Change-Id: Ie11155632c1a627a1c3303555a6ba10926c7efb0

pyghmi/ipmi/command.py

@@ -140,6 +140,7 @@ class Command(object):
         self.bmc = bmc
         self._sdr = None
         self._oem = None
+        self._oemknown = False
         self._netchannel = None
         self._ipv6support = None
         self.certverify = None
@@ -220,9 +221,10 @@ class Command(object):
         method does an interrogation to identify the OEM.
 
         """
-        if self._oem:
+        if self._oemknown:
             return
-        self._oem = get_oem_handler(self._get_device_id(), self)
+        self._oem, self._oemknown = get_oem_handler(self._get_device_id(),
+                                                    self)
 
     def get_bootdev(self):
         """Get current boot device override information.

pyghmi/ipmi/oem/lookup.py

@@ -26,6 +26,7 @@ oemmap = {
 
 def get_oem_handler(oemid, ipmicmd):
     try:
-        return oemmap[oemid['manufacturer_id']].OEMHandler(oemid, ipmicmd)
+        return (oemmap[oemid['manufacturer_id']].OEMHandler(oemid, ipmicmd),
+                True)
     except KeyError:
-        return generic.OEMHandler(oemid, ipmicmd)
+        return generic.OEMHandler(oemid, ipmicmd), False