Automatic merge from submit-queue (batch tested with PRs 51105, 51097, 51110, 50843, 51107)

azure: Use VolumeHost.GetExec() to execute stuff in volume plugins

**What this PR does / why we need it**:

This PR updates Azure volume plugin to use `VolumeHost.GetExec()` to execute utilities like mkfs and lsblk instead of simple `os/exec`. This prepares the volume plugin to run these utilities in containers instead of running them on the host + makes the volume plugin more independent and less hardcoded.

See proposal in https://github.com/kubernetes/community/pull/589.

Note that this PR does **not** change place where utilities are executed - `VolumeHost.GetExec()` still leads directly to `os/exec`. It will be changed when the aforementioned proposal is merged and implemented.

To simplify testing, `/sys/bus/scsi/devices/*/model` and `.../vendor` are read using `ioutil.ReadFile` instead of `/bin/cat` in the first commit.

```release-note
NONE
```

@kubernetes/sig-storage-pr-reviews @kubernetes/sig-azure-misc