Use POST method instead of DELETE when erasing a build

Discussion:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2560#note_3742042

app/views/projects/builds/show.html.haml

@@ -122,7 +122,7 @@
 
                 - if @build.erasable?
                   = link_to erase_namespace_project_build_path(@project.namespace, @project, @build),
-                            class: 'btn btn-sm btn-warning', method: :delete,
+                            class: 'btn btn-sm btn-warning', method: :post,
                             data: { confirm: 'Are you sure you want to erase this build?' } do
                     = icon('eraser')
                     Erase

config/routes.rb

@@ -617,7 +617,7 @@ Rails.application.routes.draw do
             get :status
             post :cancel
             post :retry
-            delete :erase, path: :content
+            post :erase
           end
 
           resource :artifacts, only: [] do

doc/api/builds.md

@@ -344,20 +344,20 @@ Example of response
 Erase a single build of a project (remove build artifacts and a build trace)
 
 ```
-DELETE /projects/:id/builds/:build_id/content
+POST /projects/:id/builds/:build_id/erase
 ```
 
 Parameters
 
 | Attribute   | Type    | required | Description         |
-|-----------|---------|----------|---------------------|
+|-------------|---------|----------|---------------------|
 | `id`        | integer | yes      | The ID of a project |
 | `build_id`  | integer | yes      | The ID of a build   |
 
 Example of request
 
 ```
-curl -X DELETE -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" "https://gitlab.example.com/api/v3/projects/1/builds/1/content"
+curl -X POST -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" "https://gitlab.example.com/api/v3/projects/1/builds/1/erase"
 ```
 
 Example of response

lib/api/builds.rb

@@ -130,15 +130,15 @@ module API
       #   id (required) - the id of a project
       #   build_id (required) - the id of a build
       # example Request:
-      #  delete  /projects/:id/build/:build_id/content
-      delete ':id/builds/:build_id/content' do
+      #  post  /projects/:id/build/:build_id/erase
+      post ':id/builds/:build_id/erase' do
         authorize_update_builds!
 
         build = get_build(params[:build_id])
         return not_found!(build) unless build
         return forbidden!('Build is not erasable!') unless build.erasable?
 
-        build.erase!
+        build.erase
         present build, with: Entities::Build,
                        user_can_download_artifacts: can?(current_user, :download_build_artifacts, user_project)
       end

spec/requests/api/builds_spec.rb

@@ -170,16 +170,16 @@ describe API::API, api: true  do
     end
   end
 
-  describe 'DELETE /projects/:id/builds/:build_id/content' do
+  describe 'POST /projects/:id/builds/:build_id/erase' do
     before do
-      delete api("/projects/#{project.id}/builds/#{build.id}/content", user)
+      post api("/projects/#{project.id}/builds/#{build.id}/erase", user)
     end
 
     context 'build is erasable' do
       let(:build) { create(:ci_build_with_trace, :artifacts, :success, project: project, commit: commit) }
 
       it 'should erase build content' do
-        expect(response.status).to eq 200
+        expect(response.status).to eq 201
         expect(build.trace).to be_empty
         expect(build.artifacts_file.exists?).to be_falsy
         expect(build.artifacts_metadata.exists?).to be_falsy