{AKS} Fix failed live test case and add custom virtual network preparer

[FumingZhang]

Description

• Fix the “test_aks_create_default_service_with_virtual_node_addon” test case in ACS module which would fail in live test.
  • Provide the same location as the resource group preparer
  • Provide a subnet address prefix to avoid conflicts with default AKS cluster cidr
• Add a custom "AKSCustomVirtualNetworkPreparer" to replace class "VirtualNetworkPreparer" to meet the need to provide the above required resources

Testing Guide

History Notes

[Component Name 1] BREAKING CHANGE: az command a: Make some customer-facing breaking change.
[Component Name 2] az command b: Add some customer-facing feature.

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[yonzhan]

AKS

[Juliehzl]

LGTM