Report a refused XCC web login instead of returning None

get_webclient falls off its end when /api/login answers anything but 200, so
it returned None. wc() passes that back, and thirty of the thirty-four call
sites use it unchecked, so a refused login arrived as "'NoneType' object has
no attribute 'grab_json_response'" from wherever it landed.

Raised where the failure is known, and with the status: 404 is firmware with
no web api, or a Redfish-only capture of one, while 401 is credentials it
will not take. Neither was distinguishable before.

The other four call sites are the inventory reads, and they always did check.
They answer partially when the web interface is out of reach, which is why
nodeinventory still says something useful. They ask through wc_if_available
now, so that tolerance is stated rather than resting on a None.

confluent_server/aiohmi/redfish/oem/lenovo/xcc.py

@@ -1150,6 +1150,18 @@ class OEMHandler(generic.OEMHandler):
             self.weblogging = False
         return self._wc
 
+    async def wc_if_available(self):
+        """The web client, or None where carrying on without it is meant.
+
+        Four inventory reads answer partially when the web interface is out of
+        reach, and used to say so by checking wc() for None. wc() refuses now,
+        so they ask here instead.
+        """
+        try:
+            return await self.wc()
+        except pygexc.UnsupportedFunctionality:
+            return None
+
     async def get_webclient(self, login=True):
         wc = self.webclient.dupe()
         wc.vintage = util._monotonic_time()
@@ -1179,6 +1191,12 @@ class OEMHandler(generic.OEMHandler):
                     wc.set_header('X-XSRF-TOKEN', cookie.value)
                     break
             return wc
+        # Falling off the end returned None, which wc() handed to thirty
+        # call sites that use it unchecked. The status separates firmware
+        # with no web api, answering 404, from credentials it will not take.
+        raise pygexc.UnsupportedFunctionality(
+            'the XCC web interface, which this operation needs beside '
+            'Redfish, did not accept a login (HTTP {0})'.format(status))
 
     async def grab_redfish_response_with_status(self, url, body=None, method=None):
         wc = self.webclient
@@ -1818,7 +1836,7 @@ class OEMHandler(generic.OEMHandler):
             if self.updating:
                 raise pygexc.TemporaryError(
                     'Cannot read extended inventory during firmware update')
-            wc = await self.wc()
+            wc = await self.wc_if_available()
             if wc:
                 adapterdata = await wc.grab_json_response(self.ADP_URL)
                 if adapterdata:
@@ -1897,7 +1915,7 @@ class OEMHandler(generic.OEMHandler):
         # mode 0 is firmware, 1 is hardware
         storagedata = self.get_cached_data('lenovo_cached_storage')
         if not storagedata:
-            wc = await self.wc()
+            wc = await self.wc_if_available()
             if wc:
                 storagedata = await wc.grab_json_response(
                     '/api/function/raid_alldevices?params=storage_GetAllDisks')
@@ -1926,7 +1944,7 @@ class OEMHandler(generic.OEMHandler):
     async def _get_cpu_inventory(self):
         procdata = self.get_cached_data('lenovo_cached_proc')
         if not procdata:
-            wc = await self.wc()
+            wc = await self.wc_if_available()
             if wc:
                 procdata = await wc.grab_json_response(
                     '/api/dataset/imm_processors')
@@ -1944,7 +1962,7 @@ class OEMHandler(generic.OEMHandler):
     async def _get_mem_inventory(self):
         memdata = self.get_cached_data('lenovo_cached_memory')
         if not memdata:
-            wc = await self.wc()
+            wc = await self.wc_if_available()
             if wc:
                 memdata = await wc.grab_json_response(
                     '/api/dataset/imm_memory')