Fix margin issue between buttons on pipeline page

What does this MR do?

Fix a margin between two buttons, as requested in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9391#note_24068315

Are there points in the code the reviewer needs to double check?

There was an extra whitespace character between the buttons that didn't appear in other places. Really hard to track it down. Finally I followed an example from app/views/projects/commit/_commit_box.html.haml and put the text for the Retry button in a do loop in the Haml file, and that got rid of the space. Weird...

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together