logging: Sort files when pruning old logs

Currently this logging implementation is dependent on the order of files
as returned by filepath.Glob, which although internal methods are
documented to be lexographical, does not publicly document this. Here we
defensively resort.

command/agent/log_file.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -104,6 +105,11 @@ func (l *logFile) pruneFiles() error {
 	if err != nil {
 		return err
 	}
+
+	// Stort the strings as filepath.Glob does not publicly guarantee that files
+	// are sorted, so here we add an extra defensive sort.
+	sort.Strings(matches)
+
 	// Prune if there are more files stored than the configured max
 	stale := len(matches) - l.MaxFiles
 	for i := 0; i < stale; i++ {

command/agent/log_file_test.go

@@ -140,7 +140,7 @@ func TestLogFile_deleteArchives(t *testing.T) {
 		}
 		contents := string(bytes)
 
-		require.NotEqual("[INFO] Hellow World", contents, "oldest log should have been deleted")
+		require.NotEqual("[INFO] Hello World", contents, "oldest log should have been deleted")
 	}
 }