provider/Azure: various bugfixes

[aznashwan]

• added instance flag to clearly denote whether an instance had a custom hosted_service created for it to avoid the deletion of one if it was created separately but given the same name as the instance.
• added wait on instance deletion for associated blob deletion; fixes Azure provider: blob lease conflict when reprovisioning instances #3109; fixes part of Azure provider unable to delete multiple resources #2416
• added guarding Mutex for secgroup-rule-related concurrent operations; fixes Azure provider: failure due concurrent access when requires exclusive access to Network Security Group #3111
• added usage warning on secgroup rules; addresses part of Azure provider: failure due concurrent access when requires exclusive access to Network Security Group #3111

I cannot thank @keymon enough for the most absolutely outrageously amazing bug reports I've received in my life.

[phinze]

Can we toss an outer limit timeout on this?

We have a resource.Retry helper that's commonly used elsewhere for this purpose:

https://github.com/hashicorp/terraform/blob/master/helper/resource/wait.go#L12-L36

Example usage:

https://github.com/hashicorp/terraform/blob/master/builtin/providers/aws/resource_aws_autoscaling_group.go#L374-L394

[phinze]

One comment - otherwise this LGTM!

[aznashwan]

@phinze: I should really spend a day or two in the helper package; at least it'll preventing me from re-inventing wheels which are square compared to you guys' 😄

[phinze]

Is this error retryable? If you want the error to break the Retry loop immediately, wrap it in a resource.RetryError

[aznashwan]

@phinze: good catch on that! Updated and ready to go 😄

[phinze]

LGTM! Merging...

[ghost]

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