Do not append yaml file to args if Action is a gcloudGroup

[brianfoshee]

Actions like gcloud app services list will fail with the addition of a
yaml file argument because it's arbitrary and unnecessary.

Use case:
I am trying to use gcloud app services set-traffic but I see the error:

ERROR: (gcloud.app.services.list) unrecognized arguments: ./app.yaml 

The command is configured properly with the exception of the app.yaml arg:

Running Command: gcloud app services set-traffic ./app.yaml MY_SERVICE --project MY_PROJECT --quiet --migrate --splits MY_COMMIT_SHA=1

Drone step is setup as follows:

- name: migrate-traffic
  pull: if-not-exists
  image: nytimes/drone-gae
  settings:
    action: services
    sub_commands: set-traffic
    addl_flags:
    - --migrate
    - --splits ${DRONE_COMMIT_SHA:0:8}=1
    project: MY_PROJECT
    service: MY_SERVICE
  environment:
    GAE_CREDENTIALS:
      from_secret: MY_CREDENTIALS
  when:
    event:
    - tag

None of the help docs for the commands in gcloudGroup point to the use of a yaml file so this should not break anything.

$ gcloud help app services
$ gcloud help app instances
$ gcloud help app versions