Code cleanup in tests

Replaced such pattern:
    Entry entry = TestCaseUtils.makeEntry(ldifLines);
    AddOperation addOperation = getRootConnection().processAdd(entry);
    assertEquals(addOperation.getResultCode(), ResultCode.SUCCESS);
    assertNotNull(DirectoryServer.getEntry(entry.getName()));

with the follwing code:
    Entry entry = TestCaseUtils.addEntry(ldifLines);

and modified TestCaseUtils.addEntry() to:
1) return the added entry
2) check that DirectoryServer.getEntry() can find the newly added entry