[MM-31360] downgrade error logs which doesn't break the flow (#16612)

* downgrade error logs which doesn't break the flow

* reflect revivew comments

services/upgrader/upgrader_linux.go

@@ -81,25 +81,25 @@ func getCurrentVersionTgzUrl() string {
 func verifySignature(filename string, sigfilename string, publicKey string) error {
 	keyring, err := openpgp.ReadArmoredKeyRing(bytes.NewReader([]byte(publicKey)))
 	if err != nil {
-		mlog.Error("Unable to load the public key to verify the file signature", mlog.Err(err))
+		mlog.Debug("Unable to load the public key to verify the file signature", mlog.Err(err))
 		return NewInvalidSignature()
 	}
 
 	mattermost_tar, err := os.Open(filename)
 	if err != nil {
-		mlog.Error("Unable to open the Mattermost .tar file to verify the file signature", mlog.Err(err))
+		mlog.Debug("Unable to open the Mattermost .tar file to verify the file signature", mlog.Err(err))
 		return NewInvalidSignature()
 	}
 
 	signature, err := os.Open(sigfilename)
 	if err != nil {
-		mlog.Error("Unable to open the Mattermost .sig file verify the file signature", mlog.Err(err))
+		mlog.Debug("Unable to open the Mattermost .sig file verify the file signature", mlog.Err(err))
 		return NewInvalidSignature()
 	}
 
 	_, err = openpgp.CheckDetachedSignature(keyring, mattermost_tar, signature)
 	if err != nil {
-		mlog.Error("Unable to verify the Mattermost file signature", mlog.Err(err))
+		mlog.Debug("Unable to verify the Mattermost file signature", mlog.Err(err))
 		return NewInvalidSignature()
 	}
 	return nil
@@ -157,8 +157,7 @@ func canIUpgrade() error {
 
 func CanIUpgradeToE0() error {
 	if err := canIUpgrade(); err != nil {
-		mlog.Error("Unable to upgrade from TE to E0", mlog.Err(err))
-		return err
+		return errors.Wrap(err, "unable to upgrade from TE to E0")
 	}
 	if model.BuildEnterpriseReady == "true" {
 		mlog.Warn("Unable to upgrade from TE to E0. The server is already running E0.")
@@ -252,12 +251,14 @@ func download(url string, limit int64) (string, error) {
 func getFilePermissionsOrDefault(filename string, def os.FileMode) os.FileMode {
 	file, err := os.Open(filename)
 	if err != nil {
-		mlog.Error("Unable to get the file permissions", mlog.String("filename", filename), mlog.Err(err))
+		mlog.Warn("Unable to get the file permissions", mlog.String("filename", filename), mlog.Err(err))
 		return def
 	}
+	defer file.Close()
+
 	fileStats, err := file.Stat()
 	if err != nil {
-		mlog.Error("Unable to get the file permissions", mlog.String("filename", filename), mlog.Err(err))
+		mlog.Warn("Unable to get the file permissions", mlog.String("filename", filename), mlog.Err(err))
 		return def
 	}
 	return fileStats.Mode()