Discard disused webclient

In some environments, this was keeping a stale file
descriptor alive.

Change-Id: Iad94c9dc6a7bb46dce6d7597e1639e127363c5b9

pyghmi/ipmi/oem/lenovo/imm.py

@@ -1544,6 +1544,8 @@ class XCCClient(IMMClient):
             self.fwo = None
         if self._keepalivesession:
             self._refresh_token_wc(self._keepalivesession)
+        elif self._wc:
+            self._wc = None
 
     def fetch_psu_firmware(self):
         psudata = self.get_cached_data('lenovo_cached_psu')