e2e: Increase disk size to 40G for openshift story

Looks like with 4.15, free disk space is shrink by ~2G and node soon hit
disk pressure during this test. In this PR disk size is increased to 40G
to make sure following error doesn't happen during e2e.

```
Warning  FailedScheduling  94s   default-scheduler  0/1 nodes are available: 1 node(s) had untolerated taint {node.kubernetes.io/disk-pressure: }. preemption: 0/1 nodes are available: 1 Preemption is not helpful for scheduling..
```

test/e2e/features/story_openshift.feature

@@ -2,7 +2,8 @@
 Feature: 4 Openshift stories
 
 	Background:
-		Given ensuring CRC cluster is running
+		Given setting config property "disk-size" to value "40" succeeds
+		And ensuring CRC cluster is running
 		And ensuring oc command is available
 		And ensuring user is logged in succeeds