Maint: do not mock os functions

- Use filepaths with /tmp for tests instead
- Only mock functions where filepath can't be specified such as user.Lookup

internal/provider/provider.go

@@ -30,7 +30,6 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/vyprvpn"
 	"github.com/qdm12/gluetun/internal/provider/windscribe"
 	"github.com/qdm12/golibs/logging"
-	"github.com/qdm12/golibs/os"
 )
 
 // Provider contains methods to read and modify the openvpn configuration to connect as a client.
@@ -38,7 +37,7 @@ type Provider interface {
 	GetOpenVPNConnection(selection configuration.ServerSelection) (connection models.OpenVPNConnection, err error)
 	BuildConf(connection models.OpenVPNConnection, username string, settings configuration.OpenVPN) (lines []string)
 	PortForward(ctx context.Context, client *http.Client,
-		openFile os.OpenFileFunc, pfLogger logging.Logger, gateway net.IP, fw firewall.Configurator,
+		pfLogger logging.Logger, gateway net.IP, fw firewall.Configurator,
 		syncState func(port uint16) (pfFilepath string))
 }