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fix azure disk mount failure on coreos and some other distros
**What this PR does / why we need it**:
azure disk mount failure on coreos due to `/dev/disk/azure` not populated on coreos, and also on some other distros.
After a long time back and forth discussion, I have decided to fix this issue on k8s side. Customers are leaving azure because of this udev issue, you could read details from #50150 . I have verifed the code works well on current coreos on azure.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*:
fixes#50150: azure_dd: managed disks don't pass "FormatAndMount"
In coreos on azure and some old distros, one udev rule is not applied, which means `/dev/disk/azure` not populated, while current disk detection code logic relies on `/dev/disk/azure`, so it would lead to azure disk mount failure, for more details, pls refer to #50150
**Special notes for your reviewer**:
In v1.6, there is no such issue becuase it's not using /dev/azure/disk to detect the LUN of new disk, so I refer the code logic of v1.6:
https://github.com/kubernetes/kubernetes/blob/release-1.6/pkg/volume/azure_dd/vhd_util.go#L59-L66
while from v1.7, it's using /dev/azure/disk, the code logic does not apply to distro which does not have udev rules(/dev/azure/disk), see:
https://github.com/kubernetes/kubernetes/blob/release-1.7/pkg/volume/azure_dd/azure_common.go#L231-L236
**Release note**:
```
fix azure disk mount failure on coreos and some other distro due to udev rule not applied
```
/sig azure
@rootfs @brendanburns @colemickens
@tlyng @karataliu @szarkos
59ad01f994