BBSIM http server transfer image counter

At ONU software upgrade the openonu-adapter internally stores images downloaded from the (BBSIM) http server. There are upgrade API's and error conditions with the effect of removing these images from the adapter again. Correct internal storage or new download from the BBSIM server should be verified in Robot test cases. An easy way to do this would be to evaluate the number of (successfully) transferred images by the BBSIM server (e.g. in subsequent download attempts). For the moment the BBSIM server provides only one image to the adapter which may also change in future. So it would be good to have a counter per successfully transferred image. These image counters must be able to be requested from some suitable interface that can be used within Robot test cases.