Maint: tun package to handle tun device operations

- Moved from openvpn package to tun package
- TUN check verifies Rdev value
- TUN create
- Inject as interface to main function
- Add integration test
- Clearer log message for end users if tun device does not exist
- Remove unix package (unneeded for tests)
- Remove tun file opening at the end of tun file creation
- Do not mock unix.Mkdev (no OS operation)
- Remove Tun operations from OpenVPN configurator

internal/openvpn/openvpn.go

@@ -4,7 +4,6 @@ package openvpn
 
 import (
 	"github.com/qdm12/gluetun/internal/constants"
-	"github.com/qdm12/gluetun/internal/unix"
 	"github.com/qdm12/golibs/command"
 	"github.com/qdm12/golibs/logging"
 )
@@ -12,7 +11,6 @@ import (
 type Configurator interface {
 	VersionGetter
 	AuthWriter
-	TUNCheckCreater
 	Starter
 }
 
@@ -24,18 +22,14 @@ type StarterAuthWriter interface {
 type configurator struct {
 	logger       logging.Logger
 	cmder        command.RunStarter
-	unix         unix.Unix
 	authFilePath string
-	tunDevPath   string
 }
 
-func NewConfigurator(logger logging.Logger, unix unix.Unix,
+func NewConfigurator(logger logging.Logger,
 	cmder command.RunStarter) Configurator {
 	return &configurator{
 		logger:       logger,
 		cmder:        cmder,
-		unix:         unix,
 		authFilePath: constants.OpenVPNAuthConf,
-		tunDevPath:   constants.TunnelDevice,
 	}
 }