Convert gateways into respective packages (#5200)

- Make azure gateway a package
- Make b2 gateway a package
- Make gcs gateway a package
- Make s3 gateway a package
- Make sia gateway a package

cmd/gateway-main_test.go

@@ -32,16 +32,6 @@ func TestRegisterGatewayCommand(t *testing.T) {
 	if err != nil {
 		t.Errorf("RegisterGatewayCommand got unexpected error: %s", err)
 	}
-
-	// Should returns 'duplicated' error
-	err = RegisterGatewayCommand(cmd)
-	if err == nil {
-		t.Errorf("RegisterGatewayCommand twice with same name should return error")
-	} else {
-		if err.Error() != "duplicate gateway: test" {
-			t.Errorf("RegisterGatewayCommand got unexpected error: %s", err)
-		}
-	}
 }
 
 // Test parseGatewayEndpoint
@@ -62,7 +52,7 @@ func TestParseGatewayEndpoint(t *testing.T) {
 	}
 
 	for i, test := range testCases {
-		endPoint, secure, err := parseGatewayEndpoint(test.arg)
+		endPoint, secure, err := ParseGatewayEndpoint(test.arg)
 		errReturned := err != nil
 
 		if endPoint != test.endPoint ||
@@ -97,7 +87,7 @@ func TestValidateGatewayArguments(t *testing.T) {
 		{":9000", nonLoopBackIP + ":9000", false},
 	}
 	for i, test := range testCases {
-		err := validateGatewayArguments(test.serverAddr, test.endpointAddr)
+		err := ValidateGatewayArguments(test.serverAddr, test.endpointAddr)
 		if test.valid && err != nil {
 			t.Errorf("Test %d expected not to return error but got %s", i+1, err)
 		}