Code maintenance: OS package for file system

- OS custom internal package for file system interaction
- Remove fileManager external dependency
- Closer API to Go's native API on the OS
- Create directories at startup
- Better testability
- Move Unsetenv to os interface

internal/params/params.go

@@ -2,11 +2,10 @@ package params
 
 import (
 	"net"
-	"os"
 	"time"
 
 	"github.com/qdm12/gluetun/internal/models"
-	"github.com/qdm12/golibs/files"
+	"github.com/qdm12/gluetun/internal/os"
 	"github.com/qdm12/golibs/logging"
 	libparams "github.com/qdm12/golibs/params"
 	"github.com/qdm12/golibs/verification"
@@ -128,22 +127,20 @@ type Reader interface {
 }
 
 type reader struct {
-	envParams   libparams.EnvParams
-	logger      logging.Logger
-	verifier    verification.Verifier
-	unsetEnv    func(key string) error
-	fileManager files.FileManager
+	envParams libparams.EnvParams
+	logger    logging.Logger
+	verifier  verification.Verifier
+	os        os.OS
 }
 
 // Newreader returns a paramsReadeer object to read parameters from
 // environment variables.
-func NewReader(logger logging.Logger, fileManager files.FileManager) Reader {
+func NewReader(logger logging.Logger, os os.OS) Reader {
 	return &reader{
-		envParams:   libparams.NewEnvParams(),
-		logger:      logger,
-		verifier:    verification.NewVerifier(),
-		unsetEnv:    os.Unsetenv,
-		fileManager: fileManager,
+		envParams: libparams.NewEnvParams(),
+		logger:    logger,
+		verifier:  verification.NewVerifier(),
+		os:        os,
 	}
 }