Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Fix test images

These commits fix volume_io tests for iSCSI and Ceph RBD. Both server images were quite old (Fedora 22), so I updated them to ~~something more stable (CentOS 7) and to newer Ceph (Jewel, 10.2.7).~~ something newer (Fedora 26).

The most important fix is that the test volumes have 120 MB so volume_io test can actually run - the tests put 100MB file to the volume to check its persistence.

When mount containers in #53440 are merged I'll try to run the tests regularly with every PR (or merge) so we catch regressions quickly.

```release-note
NONE
```

/sig testing
/sig storage

/assign @jeffvance 

Fixes: #56725