Transient failures in spec/features/projects/wiki/markdown_preview_spec.rb

As seen in https://gitlab.com/gitlab-org/gitlab-ce/builds/16735563:

  1) Projects > Wiki > User previews markdown changes while creating a new wiki page when there are spaces in the page name rewrites relative links as expected
     Failure/Error: click_link 'New page'

     Capybara::ElementNotFound:
       Unable to find link "New page"
     # ./spec/features/projects/wiki/markdown_preview_spec.rb:49:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:76:in `block (2 levels) in <top (required)>'

Finished in 15 minutes 19 seconds (files took 15.55 seconds to load)
346 examples, 1 failure

Failed examples:

rspec ./spec/features/projects/wiki/markdown_preview_spec.rb:48 # Projects > Wiki > User previews markdown changes while creating a new wiki page when there are spaces in the page name rewrites relative links as expected

and https://gitlab.com/gitlab-org/gitlab-ce/builds/16738363:

  1) Projects > Wiki > User previews markdown changes while creating a new wiki page when there are no spaces or hyphens in the page name rewrites relative links as expected
     Failure/Error: find('.add-new-wiki').trigger('click')

     Capybara::ElementNotFound:
       Unable to find css ".add-new-wiki"
     # ./spec/features/projects/wiki/markdown_preview_spec.rb:27:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:76:in `block (2 levels) in <top (required)>'

Finished in 17 minutes 52 seconds (files took 19.1 seconds to load)
346 examples, 1 failure

Failed examples:

rspec ./spec/features/projects/wiki/markdown_preview_spec.rb:26 # Projects > Wiki > User previews markdown changes while creating a new wiki page when there are no spaces or hyphens in the page name rewrites relative links as expected