Description of problem:
The installer fails with an error when deleting the bootstrap node.

Version-Release number of the following components:
4.2.0-0.nightly-2019-09-11-114314
./openshift-install v4.2.0
built from commit 3f34b38a1a6888bcc64c23f73cee3a7039cb8a70
release image quay.io/openshift-release-dev/ocp-release-nightly@sha256:9b5d0863abafcb98d1be5a4cf153e919530ba79ea4b18c390d602f9284cf916b

How reproducible:
This happened the 3 times that I have attempted an install. The first two times where using the slack cluster-bot. The third time was manually running the installer.

Actual results:
DEBUG module.bootstrap.azurerm_virtual_machine.bootstrap: Still destroying... [id=/subscriptions/8c20ec23-8478-4f46-96f4-...rtualMachines/mstaeble-9k9gg-bootstrap, 1m30s elapsed] 
DEBUG module.bootstrap.azurerm_virtual_machine.bootstrap: Destruction complete after 1m34s 
ERROR                                              
ERROR Error: Error waiting for removal of Backend Address Pool Association for NIC "mstaeble-9k9gg-bootstrap-nic" (Resource Group "mstaeble-9k9gg-rg"): Code="OperationNotAllowed" Message="Operation 'startTenantUpdate' is not allowed on VM 'mstaeble-9k9gg-bootstrap' since the VM is marked for deletion. You can only retry the Delete operation (or wait for an ongoing one to complete)." Details=[] 
ERROR                                              
ERROR                                              
FATAL Terraform destroy: failed to destroy using Terraform 

Additional info:
OpenShift does install successfully. It is only that the installer returns with a failure and may not be completely destroying all of the bootstrap resources.