feature: add ExecConfig validation rule in swagger

[allencloud]

Signed-off-by: Allen Sun allensun.shl@alibaba-inc.com

1.Describe what this PR did

This PR restricts the validate type Post request config body.

• I add ExecCreateConfig field restriction in swagger.yml;
• generate structs in apis/types, in this struct file, there are validation funcs which takes restriction into consideration:

func (m *ExecCreateConfig) validateCmd(formats strfmt.Registry) error {

	if swag.IsZero(m.Cmd) { // not required
		return nil
	}

	iCmdSize := int64(len(m.Cmd))

	if err := validate.MinItems("Cmd", "body", iCmdSize, 1); err != nil {
		return err
	}

	return nil
}

When the above two aspects has been done, codes in https://github.com/alibaba/pouch/blob/master/apis/server/container_bridge.go#L56 will work.

	config := &types.ExecCreateConfig{}
	// decode request body
	if err := json.NewDecoder(req.Body).Decode(config); err != nil {
		return httputils.NewHTTPError(err, http.StatusBadRequest)
	}
	// validate request body
	if err := config.Validate(strfmt.NewFormats()); err != nil {
		return httputils.NewHTTPError(err, http.StatusBadRequest)
	}

2.Does this pull request fix one issue?
none, this is related to issue #443.

3.Describe how you did it
NONE

4.Describe how to verify it
We need to add test cases according to this PR in API POST /containers/{id}/exec test.
/cc @Letty5411

5.Special notes for reviews

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[Letty5411]

@allencloud I'll add a nil CMD check for exec API.

[skoowoo]

LGTM