Automatic merge from submit-queue (batch tested with PRs 47066, 48892, 48933, 48854, 48894)
azure: msi: add managed identity field, logic
**What this PR does / why we need it**: Enables managed service identity support for the Azure cloudprovider. "Managed Service Identity" allows us to ask the Azure Compute infra to provision an identity for the VM. Users can then retrieve the identity and assign it RBAC permissions to talk to Azure ARM APIs for the purpose of the cloudprovider needs.
Per the commit text:
```
The azure cloudprovider will now use the Managed Service Identity
to retrieve access tokens for the Azure ARM APIs, rather than
requiring hard-coded, user-specified credentials.
```
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: n/a
**Special notes for your reviewer**: none
**Release note**:
```release-note
azure: support retrieving access tokens via managed identity extension
```
cc: @brendandburns @jdumars @anhowe
The azure cloudprovider will now use the Managed Service Identity
to retrieve access tokens for the Azure ARM APIs, rather than
requiring hard-coded, user-specified credentials.
Automatic merge from submit-queue (batch tested with PRs 48594, 47042, 48801, 48641, 48243)
Add initial support for the Azure instance metadata service.
Part of fixing #46632
@colemickens @rootfs @jdumars @kris-nova
- leveraging Config struct (—cloud-config) to store backoff and rate limit on/off and performance configuration
- added add’l error logging
- enabled backoff for vm GET requests
An initial attempt at engaging exponential backoff for API error responses.
Uses k8s.io/client-go/util/flowcontrol; implementation inspired by GCE
cloudprovider backoff.
The default polling delay of 1 minute results in very long delays when
an Azure Disk is attached to a node. It gets worse as go-autorest
doubles the default delay to 2 minutes.
Please see: https://github.com/kubernetes/kubernetes/issues/35180#issuecomment-273085063
Only the PollingDelay for VirtualMachinesClient is modified here to
avoid too much pressure on Azure quotas.
