[SP-1621] - Regression of MONDRIAN-2230 - XMLA fails to be read if a prior schema is not valid due to a broken jdbc connection (5.2 Suite)

@lucboudreau would you mind to review/merge
there are two commits: 
 - the first one change XMLA unit test so that they fail
 - the second one provides the fix. It also has quite big comment - I would appreciate if you take a look.