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

git-svn-id: https://svn.forgerock.org/opendj/branches/opendj3-server-dev@11101 41b1ffd8-f28e-4786-ab96-9950f0a78031
Chasing random test.


TasksTestCase.java:
Reverted the code to not use SoftAssertions + added more info in case of failure.

TestBackupAndRestore.java:
Extracted methods backupTask() and restoreTask() to hide common data.

git-svn-id: https://svn.forgerock.org/opendj/branches/opendj3-server-dev@11102 41b1ffd8-f28e-4786-ab96-9950f0a78031