Specify disk size when attaching unmanaged disks

[bingosummer]

• Please check this box once you have run the unit tests

  pushd src/bosh_azure_cpi
    bundle install
    bundle exec rspec spec/unit/*
  popd
  

523 examples, 0 failures. 2509 / 2749 LOC (91.27%) covered. => 525 examples. 2520 / 2760 LOC (91.3%) covered.

Changelog

• Specify the disk size when attaching an unmanaged disk. Otherwise, the disk size can't be shown by Azure Portal or Azure CLI.
• Returns lun directly when attaching disks in azure_client2

[cfdreddbot]

Hey bingosummer!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.