Fix userkey create.

[shawn111]

What this PR does / why we need it:
echo "ssh-rsa key ..." | ssh localhost -p 2222 -l admin userkey create shawn
Without the PR, it shows error: Key: non zero value required;AuthorizedKey: non zero value required;
For the AuthorizedKey, I compared the code in ssh.go, I thought it might be missing.

For the Key, it is a []byte field. The required valid cause Key: non zero value required.

Which issue this PR fixes: fixes #xxx, fixes #xxx...
fixes #46
Special notes for your reviewer:

--- a/db.go
+++ b/db.go
@@ -70,7 +70,7 @@ type Host struct {
 // UserKey defines a user public key used by sshportal to identify the user
 type UserKey struct {
        gorm.Model
-       Key           []byte `sql:"size:10000" valid:"required,length(1|10000)"`
+       Key           []byte `sql:"size:10000" valid:"length(1|10000)"` // FIXME
        AuthorizedKey string `sql:"size:10000" valid:"required,length(1|10000)"`
        UserID        uint   ``
        User          *User  `gorm:"ForeignKey:UserID"`
(END)

[shawn111]

Hi @moul,

I used isEmptyValue to test the field, userkey.Key.
Even it is not Empty but it is a []byte field.
govalidator.ValidateStruct would check each byte in the userkey.Key, the required check would be wrong.

func isEmptyValue(v reflect.Value) bool {
        switch v.Kind() {
        case reflect.String, reflect.Array:
                return v.Len() == 0
        case reflect.Map, reflect.Slice:
                return v.Len() == 0 || v.IsNil()
        case reflect.Bool:
                return !v.Bool()
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                return v.Int() == 0
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                return v.Uint() == 0
        case reflect.Float32, reflect.Float64:
                return v.Float() == 0
        case reflect.Interface, reflect.Ptr:
                return v.IsNil()
        }

        return reflect.DeepEqual(v.Interface(), reflect.Zero(v.Type()).Interface())
}

[moul]

LGTM