Change Retry link to point to the self service interface

• replaced retry link to /user/:user/retry/<%= test.run_id %> in history.erb.
• added redirect in GET /:user/retry/:run_id to itself but with @user.username in place of :user.
• removed before block in api.rb containing read_request_user since user is authenticated only using key in api.rb.
• changed GET /api/v1/retry/:run_id to redirect directly to /:user/retry/:run_id.
• added and updated tests in spec/debci/api_spec.rb and spec/debci/self_service_spec.rb.

Closes: #179 (closed)