fix ESASKY tests by marking the huge data download as bigdata, skipping suzaku (which has no hits), and xfailing a failing HST test that appears to be a remote issue.  Added a new small-data test for the image retrieval too.
fix ESASKY tests by marking the huge data download as bigdata, skipping
suzaku (which has no hits), and xfailing a failing HST test that appears
to be a remote issue.  Added a new small-data test for the image
retrieval too.

imbasimba/astroquery,ceb8/astroquery,imbasimba/astroquery,ceb8/astroquery