ParserTests: set page name for all tests (since env is reused)

* When I was updating parser tests with updates to data-mw, I was
  getting strange failures which I narrowed down to updates to
  relativeLinkPrefix (as part of setPageName). parser-tests reuses
  the same env object for all tests => it should set page name
  for all tests.

Change-Id: Iffbab8bc773c6305702f9a82afc6f294bc5b0efd