Gracefully handle degraded instances in verification

The current code assumes that every instance either is of type
diskless or has at least one disk. However, with the option to
remove individual disk degraded 0-disk non-diskless instances
can occur. While such instances usually are not useful, Ganeti
still should be operational in their presence.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Hrvoje Ribicic <riba@google.com>

lib/cmdlib/cluster.py

@@ -2618,6 +2618,7 @@ class LUClusterVerifyGroup(LogicalUnit, _VerifyErrors):
     node_disks = {}
     node_disks_devonly = {}
     diskless_instances = set()
+    nodisk_instances = set()
     diskless = constants.DT_DISKLESS
 
     for nuuid in node_uuids:
@@ -2630,6 +2631,8 @@ class LUClusterVerifyGroup(LogicalUnit, _VerifyErrors):
                for disk in instanceinfo[inst_uuid].disks]
 
       if not disks:
+        nodisk_instances.update(uuid for uuid in node_inst_uuids
+                                if instanceinfo[uuid].disk_template != diskless)
         # No need to collect data
         continue
 
@@ -2687,6 +2690,10 @@ class LUClusterVerifyGroup(LogicalUnit, _VerifyErrors):
     for inst_uuid in diskless_instances:
       assert inst_uuid not in instdisk
       instdisk[inst_uuid] = {}
+    # ...and disk-full instances that happen to have no disks
+    for inst_uuid in nodisk_instances:
+      assert inst_uuid not in instdisk
+      instdisk[inst_uuid] = {}
 
     assert compat.all(len(statuses) == len(instanceinfo[inst].disks) and
                       len(nuuids) <= len(instanceinfo[inst].all_nodes) and