Openshift fails when related images are defined but empty string

This error occurs in current versions of Openshift which do not yet seem to provide related image values to the operator as mentioned in  K8S-1284.

The fix is to simply use the default spec values whenever we come across an empty string.

Supposedly Openshift 4.4 will provide us actual values, but this is not the case in 4.3.

As a result cluster fails to start with error "invalid image string: ", because we are expecting olm to pass a value that it may not actually provide.