Pr to support managed 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
  

Changelog

• Support managed disks
• Upgrade azure-storage-ruby to v0.11.5

Close #228: Can we support managed disks?
Close #225: Stripe storage account placement across each VM in an availability set
Close #178: Avoid using storage account tables to keep track of copying process
Close #116: user should be able to set storage_account_name on a persistent disk
Close #68: CID of VMs is not well named

[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.