Add function to fetch a specific items inventory

It may be desirable for calling code to specifically call
out a single component.  Add the 'get_inventory_of_component' to
make that possible.

Also refine the OEM processors such that they should pass through
'None' to make some upper level code more straightforward.

Change-Id: Ic662d6c330af24fb8ed7a9cf2f8bcfd6202c1337

pyghmi/ipmi/command.py

@@ -376,6 +376,22 @@ class Command(object):
         for fruid in self._sdr.fru:
             yield self._sdr.fru[fruid].fru_name
 
+    def get_inventory_of_component(self, component):
+        """Retrieve inventory of a component
+
+        Retrieve detailed inventory information for only the requested
+        component.
+        """
+        self.oem_init()
+        if component == 'System':
+            return self._oem.process_fru(fru.FRU(ipmicmd=self).info)
+        if self._sdr is None:
+            self._sdr = sdr.SDR(self)
+        for fruid in self._sdr.fru:
+            if self._sdr.fru[fruid].fru_name == component:
+                return self._oem.process_fru(fru.FRU(
+                    ipmicmd=self, fruid=fruid, sdr=self._sdr.fru[fruid]).info)
+
     def get_inventory(self):
         """Retrieve inventory of system
 

pyghmi/ipmi/oem/generic.py

@@ -40,5 +40,7 @@ class OEMHandler(object):
         ordered lists that their expectations are not broken by an update
         """
         # In the generic case, just pass through
+        if fru is None:
+            return fru
         fru['oem_parser'] = None
         return fru

pyghmi/ipmi/oem/lenovo.py

@@ -24,6 +24,8 @@ class OEMHandler(generic.OEMHandler):
         self.oemid = oemid
 
     def process_fru(self, fru):
+        if fru is None:
+            return fru
         if (self.oemid['manufacturer_id'] == 19046 and
                 self.oemid['device_id'] == 32):
             fru['oem_parser'] = 'lenovo'