Storage checkup failed reason is not consistent for pvc and snapshot source format 

CNV4.17

always

1. Make sure the dataimportcron source format is pvc 
2. Unset the default storage class and run checkup 
3. Set multiple default storage class and run checkup 
4. Manually set the dataimportcron source format to snapshot
5. Unset the default storage class and run checkup 
6. Set multiple default storage class and run checkup 

PVC source format:
2. Checkup failed with the reason when no default storage class:
 'status.failureReason': 'no default storage class\npvc failed to bound',

3. Checkup failed with the reason when multiple storage classes:
 'status.failureReason': 'there are multiple default storage classes\n'
                         'some of the VMs failed to complete boot on time',

snapshot source format:
5. Checkup failed with the reason when no default storage class:
'status.failureReason': 'persistentvolumeclaims "vmi-under-test-mj94j-dv" not found'

6. Checkup failed with the reason when multiple storage classes:
 'status.failureReason': 'Operation cannot be fulfilled on '
                         'virtualmachineinstance.kubevirt.io '
                         '"vmi-under-test-xbc29": VMI is not running',

It is better to have consistent failed reason for both pvc and snapshot source format