xls parser test fix and code duplications cleanup

...bis/systemtest/plugin/excelimport/AbstractImportTest.java

...systemtest/plugin/excelimport/ImportDatasetTypesTest.java

...temtest/plugin/excelimport/ImportExperimentTypesTest.java

.../systemtest/plugin/excelimport/ImportExperimentsTest.java

...nbis/systemtest/plugin/excelimport/ImportFromCsvTest.java

...bis/systemtest/plugin/excelimport/ImportProjectsTest.java

...ystemtest/plugin/excelimport/ImportPropertyTypesTest.java

.../systemtest/plugin/excelimport/ImportSampleTypesTest.java

...nbis/systemtest/plugin/excelimport/ImportSamplesTest.java

...enbis/systemtest/plugin/excelimport/ImportSpacesTest.java

...temtest/plugin/excelimport/ImportVocabularyTypesTest.java

...limport/test_files/experiment_types/normal_experiment.xls

.../test_files/experiment_types/normal_experiment_update.xls