Use more robust logstreamer file match

This patch improves the heka configuration to support the case where
libvirt directory is not created.

Change-Id: I95806601fc132bba4380e57a21cc8efc0c37bdc3
diff --git a/nova/meta/heka.yml b/nova/meta/heka.yml
index 9373302..cd8dba8 100644
--- a/nova/meta/heka.yml
+++ b/nova/meta/heka.yml
@@ -26,8 +26,8 @@
     {%- if pillar.nova.compute is defined %}
     libvirt_log:
       engine: logstreamer
-      log_directory: "/var/log/libvirt"
-      file_match: 'libvirtd.log'
+      log_directory: "/var/log"
+      file_match: 'libvirt/libvirtd.log'
       differentiator: ['libvirt']
       decoder: "libvirt_decoder"
       splitter: "TokenSplitter"