no input params workflow execution form has requried filed

[Huang.Xiangdong]

When execute a workflow with no input params on mistral dashboard, the execution from will show a required field with empty label.
the workflow definition is:

---
version: "2.0"

wf:
  type: direct

  tasks:
    t:
      input:
        cmd: 'cd ~ && ls'
        host: localhost
        username: stack
        password: '123'

      action: std.ssh

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/591266

[Huang.Xiangdong (privaterookie)]

I update a patch to fix this bug

https://review.openstack.org/#/c/591266/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/591266
Committed: https://git.openstack.org/cgit/openstack/mistral-dashboard/commit/?id=9f35dca96fb34f50b93aeb022524933b45ee4b2f
Submitter: Zuul
Branch: master

commit 9f35dca96fb34f50b93aeb022524933b45ee4b2f
Author: privaterookie <email address hidden>
Date: Mon Aug 13 09:44:15 2018 +0800

    fix mistral dashbaord workflow execution form bug

    fix a bug that when a workflow has no input params, execution form
    will has a requried field with empty label

    Close-bug:#1786723
    Change-Id: I49b2125ef649e94e210ff5df739684626c175172