put libvirt debug behind a flag

only turn on the libvirt debugging if we really need it, which
we could control in the gate via devstack-gate.

Change-Id: I5e6d41d5333357608ab6a614610c060400f70a10

lib/nova_plugins/hypervisor-libvirt

@@ -25,6 +25,8 @@ set +o xtrace
 
 # File injection is disabled by default in Nova.  This will turn it back on.
 ENABLE_FILE_INJECTION=${ENABLE_FILE_INJECTION:-False}
+# if we should turn on massive libvirt debugging
+DEBUG_LIBVIRT=$(trueorfalse False $DEBUG_LIBVIRT)
 
 
 # Entry Points
@@ -104,6 +106,7 @@ EOF
     add_user_to_group $STACK_USER $LIBVIRT_GROUP
 
     # Enable server side traces for libvirtd
+    if [[ "$DEBUG_LIBVIRT" = "True" ]] ; then
         local log_filters="1:libvirt 1:qemu 1:conf 1:security 3:event 3:json 3:file 1:util"
         local log_outputs="1:file:/var/log/libvirt/libvirtd.log"
         if ! grep -q "log_filters=\"$log_filters\"" /etc/libvirt/libvirtd.conf; then
@@ -112,6 +115,7 @@ EOF
         if ! grep -q "log_outputs=\"$log_outputs\"" /etc/libvirt/libvirtd.conf; then
             echo "log_outputs=\"$log_outputs\"" | sudo tee -a /etc/libvirt/libvirtd.conf
         fi
+    fi
 
     # libvirt detects various settings on startup, as we potentially changed
     # the system configuration (modules, filesystems), we need to restart