uevent: Add logs for uevents

We should not receive many hotplug uevents. Log these so we can
track what devices have been attached in the logs.

Fixes kata-containers#377

Signed-off-by: Archana Shinde <archana.m.shinde@intel.com>

agent.go

@@ -479,6 +479,8 @@ func (s *sandbox) listenToUdevEvents() {
 	}
 	defer uEvHandler.Close()
 
+	fieldLogger.Infof("Started listening for uevents")
+
 	for {
 		uEv, err := uEvHandler.Read()
 		if err != nil {
@@ -499,6 +501,8 @@ func (s *sandbox) listenToUdevEvents() {
 			"uevent-devname":   uEv.DevName,
 		})
 
+		fieldLogger.Infof("Received add uevent")
+
 		// Check if device hotplug event results in a device node being created.
 		if uEv.DevName != "" && strings.HasPrefix(uEv.DevPath, rootBusPath) {
 			// Lock is needed to safey read and modify the pciDeviceMap and deviceWatchers.