Mark failing ishare tests. See #11537
Mark intermittent tests. See #11539
Mark three consistently failing tests on hudson.

See tickets: #11541 #11542 #11543
Mark failing gatewaytest. See #11545
Removing duplicated test.

Test removed from tickets2000 in favour of test in isession.
Renamed isession test to maintain link with original ticket.
Modified xfail decorator to maintain links with existing tickets.
Merge pull request #1629 from ximenesuk/mark-failing-python-tests

Mark further failing python tests