Figure out why sometimes vmnet refuse to create interface

[sirn]

Vmnet notes:

• vmnet will refuse to create interface for some UUIDs.
  • SecureRandom.uuid (UUIDv4) hit the above bug every ~~10~~ 20 UUIDs or so created.
  • XPC_TYPE_UUID actually conforms DCE 1.1 UUIDs (per uuid(3))
    • Maybe just call xpc_uuid_create and sidestep this incompatibility altogether.
• vmnet limits single process to create only about 4-5 interfaces.
• vmnet require codesign and com.apple.vm.networking entitlement (this is why sudo is required).
• generating about 100+ vmnet interfaces will crash the host machine. (Don't)

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Test with (sudo ruby -Ilib test.rb):

require 'securerandom'
require 'vagrant-xhyve/support/vmnet_mac'

uuid = SecureRandom.uuid
puts "#{uuid} - #{VagrantPlugins::Xhyve::Support::VmnetMac.from_uuid(uuid)}"

For example, e083cf15-cbfc-4f31-a92b-0de72c86e857 reliably fails on my local machine.