Fix sequence-generator in MetaData exporter for XML Driver.
#1204 - refactored sequence-generator metadata exporting into own private method for simplicity
#1204 - using specific XML assertions to build a less-fragile test (asserting on the entire string may cause failures if the XML structure changes)
Merge branch 'hotfix/#1204-metadata-xml-exporter-should-export-sequence-generator-info'

Close #1204