Ignore files in process directoryfix/cgroup-logging

What
---
Instead of returning error of files in process directory, silently
ignore the file found.

Why
---
`PruneOldGitalyProcessDirectories` is used to delete the cgroup
directory under the `hierarchy_root` for example `/gitaly`. Inside the
cgroup directory there is always files like `cpu.stat` and
much more, so it's normal to have files in a cgroup, it's how they are
controlled.

In production we are seeing logs below which end up being noise and not
really useful:

```
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/cpuacct.usage_percpu_user","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/cpuacct.usage_sys","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/cpuacct.usage_user","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/notify_on_release","time":"2022-09-22T22:03:57.874Z"}
{"error":"gitaly process directory contains an unexpected file","level":"error","msg":"could not prune entry","path":"/sys/fs/cgroup/cpu/gitaly/tasks","time":"2022-09-22T22:03:57.874Z"}
```

Reference: https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16270
Signed-off-by: Steve Azzopardi <sazzopardi@gitlab.com>

2 files changed, 4 insertions, 7 deletions

diff --git a/internal/gitaly/config/temp_dir.go b/internal/gitaly/config/temp_dir.go
index d27100edf..96f5eb41f 100644
--- a/internal/gitaly/config/temp_dir.go
+++ b/internal/gitaly/config/temp_dir.go
@@ -26,8 +26,7 @@ func PruneOldGitalyProcessDirectories(log log.FieldLogger, directory string) err
 		log := log.WithField("path", filepath.Join(directory, entry.Name()))
 		if err := func() error {
 			if !entry.IsDir() {
-				// There should be no files, only the gitaly process directories.
-				return errors.New("gitaly process directory contains an unexpected file")
+				return nil
 			}
 
 			components := strings.Split(entry.Name(), "-")
diff --git a/internal/gitaly/config/temp_dir_test.go b/internal/gitaly/config/temp_dir_test.go
index 9961278ce..2d7076139 100644
--- a/internal/gitaly/config/temp_dir_test.go
+++ b/internal/gitaly/config/temp_dir_test.go
@@ -62,10 +62,8 @@ func TestPruneOldGitalyProcessDirectories(t *testing.T) {
 		prunableDirs = append(prunableDirs, rootRuntimeDir)
 
 		// Create an unexpected file in the runtime directory
-		unexpectedFilePath := filepath.Join(baseDir, "unexpected-file")
-		require.NoError(t, os.WriteFile(unexpectedFilePath, []byte(""), os.ModePerm))
-		expectedLogs[unexpectedFilePath] = "could not prune entry"
-		expectedErrs[unexpectedFilePath] = errors.New("gitaly process directory contains an unexpected file")
+		file := filepath.Join(baseDir, "file")
+		require.NoError(t, os.WriteFile(file, []byte(""), os.ModePerm))
 
 		nonPrunableDirs := []string{ownRuntimeDir}
 
@@ -100,7 +98,7 @@ func TestPruneOldGitalyProcessDirectories(t *testing.T) {
 		require.Equal(t, expectedLogs, actualLogs)
 		require.Equal(t, expectedErrs, actualErrs)
 
-		require.FileExists(t, unexpectedFilePath)
+		require.FileExists(t, file)
 
 		for _, nonPrunableEntry := range nonPrunableDirs {
 			require.DirExists(t, nonPrunableEntry, nonPrunableEntry)