Catch exceptions for interfaceStats in libvirt inspector

In the Libvirt inspector we call the interfaceStats()
function but there is a race between us checking if
the domain is stopped and calling interfaceStats.

This adds a try-catch around interfaceStats the
same way as is already done for blockStats etc.

Closes-Bug: #2113768
Change-Id: I25ba64f5eefe8140b45bc4ff7e20c323dc5efd79
(cherry picked from commit 70a56ba670)
Signed-off-by: Tobias Urdin <tobias.urdin@binero.com>

ceilometer/compute/virt/libvirt/inspector.py

@@ -114,7 +114,13 @@ class LibvirtInspector(virt_inspector.Inspector):
             params['interfaceid'] = interfaceid
             params['bridge'] = bridge
 
-            dom_stats = domain.interfaceStats(name)
+            try:
+                dom_stats = domain.interfaceStats(name)
+            except libvirt.libvirtError as ex:
+                LOG.warning(_("Error from libvirt when running instanceStats, "
+                              "This may not be harmful, but please check : "
+                              "%(ex)s") % {'ex': ex})
+                continue
 
             # Retrieve previous values
             prev = self.cache.get(name)

releasenotes/notes/bug-2113768-a2db3a59c8e13558.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixed `bug #2113768 <https://bugs.launchpad.net/ceilometer/+bug/2113768>`__ where
+    the Libvirt inspector did not catch exceptions thrown when calling interfaceStats
+    function on a domain.