Change project pipeline status cache key to follow project convention
Change project pipeline status cache key to follow project convention

Old cache key was: `projects/#{id}/pipeline_status/#{sha}`
New one is: `project:#{id}:pipeline_status:#{sha}`

This allows to delete any project related key just by scanning for:
`project:#{id}`.

mmkassem/gitlabhq,iiet/iiet-git,axilleas/gitlabhq,stoplightio/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,iiet/iiet-git,mmkassem/gitlabhq,dreampet/gitlab,mmkassem/gitlabhq,axilleas/gitlabhq,dreampet/gitlab,iiet/iiet-git,iiet/iiet-git,dreampet/gitlab,mmkassem/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq