User-disks are supported by QEMU and Firecracker providers.
Can be defined by using the following parameters:
```
--user-disk /mount/path:1GB
```
Can get more than 1 user disk.
Same set of user disks will be created for all master and worker nodes.
Additionally enable user-disks in qemu e2e test.
Signed-off-by: Artem Chernyshev <artem.0xD2@gmail.com>