Add flag to disable parameter validation (#595)

Set validation.Disabled to true to globally disable param validation.
This is an escape hatch to work around bugs in param validation.

autorest/validation/validation.go

@@ -24,6 +24,9 @@ import (
 	"strings"
 )
 
+// Disabled controls if parameter validation should be globally disabled.  The default is false.
+var Disabled bool
+
 // Constraint stores constraint name, target field name
 // Rule and chain validations.
 type Constraint struct {
@@ -68,6 +71,9 @@ const (
 // Validate method validates constraints on parameter
 // passed in validation array.
 func Validate(m []Validation) error {
+	if Disabled {
+		return nil
+	}
 	for _, item := range m {
 		v := reflect.ValueOf(item.TargetValue)
 		for _, constraint := range item.Constraints {