Correct idempotency for azure_rm_appserviceplan and premium SKU plans

[l3ender]

SUMMARY

This PR corrects idempotency for azure_rm_appserviceplan with premium SKU plans.

Fixes #692.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

azure_rm_appserviceplan

ADDITIONAL INFORMATION

I have corrected and added a test to verify. The tests can be ran as follows:

---
- name: "Playbook for testing."
  hosts: "localhost"
  connection: "local"
  gather_facts: false
  vars:
    resource_group: "automated-testing"
    resource_group_secondary: "automated-testing-secondary"
  collections:
    - azure.azcollection

  tasks:
    - name: "Include tests"
      include_tasks: "tests/integration/targets/azure_rm_appserviceplan/tasks/main.yml"

[l3ender]

@Fred-sun Please review...thank you!

[Fred-sun]

@l3ender Okay, we'll move forward with the merger as soon as possible. Thank you for your contribution!

[xuzhang3]

LGTM