Automatic merge from submit-queue (batch tested with PRs 50872, 51103, 51220, 51285, 50841)
ScaleIO: Use VolumeHost.GetExec() to execute stuff in volume plugins
This PR updates ScaleIO volume plugin to use `VolumeHost.GetExec()` to execute utilities like mkfs and lsblk instead of simple `os/exec` + to use a fresh `mounter` for every `SetUp` / `TearDown` calls, as they may be different each time.
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 the utilities are executed - `VolumeHost.GetExec()` still leads directly to `os/exec`. It will be changed when the aforementioned proposal is merged and implemented.
**Special notes for your reviewer**:
* I needed to pass `mount.Exec` interface from the place where it is available down to `SioClient` where it's needed to execute stuff.
@kubernetes/sig-storage-pr-reviews
/assign @vladimirvivien @rootfs
**Release note**:
```release-note
NONE
```
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