Check Azure instance state recongition

[lotas]

We observe some amount of worker was already running errors in logs.
Some of those (~100/day) are coming from workers that try to register but instance state was unexpected.
That happened because those workers were terminated by worker scanner with following reason:

failed provisioning power state; powerStates=ProvisioningState/failed/OSProvisioningClientError, PowerState/running

related changes: 4d7b4af
#3346

Maybe this is not the issue, and it behaves correctly, however the fact that worker was able to call registerWorker() shows that it probably shouldn't be stopped by worker scanner?

Azure error codes list following possible reasons for OSProvisioningClientError:

• OS Provisioning failed for VM '{0}' because the guest OS is currently being provisioned.
• OS provisioning for VM '{0}' failed. Error details: {1} Make sure the image has been properly prepared (generalized). Instructions for Windows.