Fixing failing tests in Jenkins.

SubCommandArgumentParser.java:
After r11664, getUsage(Argument) should call setUsageOrVersionDisplayed() itself.

ManageAccountTestCase.java:
Extracted method manageAccountMain(), the change to SubCommandArgumentParser will fix the tests.

DsconfigOptionsTestCase.java:
For testGenerateDoc() failure, calling DSConfig with "-?" option and "org.forgerock.opendj.gendoc" property set now returns SUCCESS while it was not before. This is due to r11664 which stops dsconfig execution after generating the documentation. This test assertion did not make sense to me.

*.java:
Code cleanup