set default event logger based on build tags

once the default event logger was removed from libpod.conf, we need to
set the default based on whether the systemd build tag is used or not.

Signed-off-by: baude <bbaude@redhat.com>

libpod/events/journal_linux.go

@@ -12,6 +12,9 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
+// DefaultEventerType is journald when systemd is available
+const DefaultEventerType = Journald
+
 // EventJournalD is the journald implementation of an eventer
 type EventJournalD struct {
 	options EventerOptions

libpod/events/journal_unsupported.go

@@ -2,6 +2,9 @@
 
 package events
 
+// DefaultEventerType is logfile when systemd is not present
+const DefaultEventerType = LogFile
+
 // newEventJournalD always returns an error if libsystemd not found
 func newEventJournalD(options EventerOptions) (Eventer, error) {
 	return nil, ErrNoJournaldLogging

libpod/runtime.go

@@ -304,7 +304,7 @@ func defaultRuntimeConfig() (RuntimeConfig, error) {
 		EnablePortReservation: true,
 		EnableLabeling:        true,
 		NumLocks:              2048,
-		EventsLogger:          "journald",
+		EventsLogger:          events.DefaultEventerType.String(),
 	}, nil
 }