poll module - new simple tests

New tests:

• that the Recent Poll block outputs the block layout rather than page layout.
• that users can vote on polls via the block
• that the 'older polls' link in the recent poll block works.
• that node is output correctly, including 'Cancel your vote' button appearing
• that only users with appropriate permission can cancel their votes
• that the 'poll' page contains the correct data.
• that polls can be edited
• the opening / closing of polls - ensuring block doesn't appear when poll is closed, and neither do the 'Vote' / 'Cancel your vote' buttons, and that the poll status is updated correctly on 'poll' page.

Dependent on tickets #474302: Poll module fixes - due to recent api changes and #372650: Poll node is not displayed when poll block is displayed as well - these tests should fail without those changes.

Cheers,
Stella