[SP-1621] - [TEST]- 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)

Unit test. Should fail before the fix has been applied.
The XmlaTestContext is changed to return a DataSource with an invalid catalog.
[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)

The fix is to skip catalog if it's not possible to enstablish a connection to the corresponding database.
This is a kind of quick-and-dirty solution.

There are several issues which cause the misbehavior:
1. MondrianCatalogHelper.generateInMemoryDatasourcesXml() returns DataSources.xml containing a single 'Pentaho' data source.
	It's not clear why each Pentaho data source is represented as a catalog within the returned datasource.
	It looks more logical to show them as a separate Mondrian data sources.
2. Even though each catalog may override connection information specified for enclosing data source - the arbitrary connection
	information is used to construct the data source object (particularly for DISCOVER_DATASOURCES XML/A request).
	See the code snippet below from FileRepository:
		            catalogInfo = datasourceInfo.catalogMap.values().iterator().next();
3. it looks a little bit strange that an OlapConnection has to be established for processing DISCOVER_DATASOURCES XML/A request.
	This is pure meta information request which should not require opening a phisical database connection.