check out original branch name instead of pr-{id}

Signed-off-by: Benjamin Cutler <bcutler@pivotal.io>

assets/lib/in.rb

@@ -19,18 +19,19 @@ def ref
 
 pr = Octokit.pull_request(input['source']['repo'], input['version']['pr'])
 id = pr['number']
+branch_ref = pr['head']['ref']
 
 system("git clone --depth 1 #{uri} #{destination} 1>&2")
 
 raise 'git clone failed' unless $CHILD_STATUS.exitstatus == 0
 
 Dir.chdir(destination) do
   system('git submodule update --init --recursive 1>&2')
-  system("git fetch -q origin pull/#{id}/head:pr-#{id} 1>&2")
-  system("git checkout pr-#{id} 1>&2")
+  system("git fetch -q origin pull/#{id}/head:#{branch_ref} 1>&2")
+  system("git checkout #{branch_ref} 1>&2")
   system("git config --add pullrequest.url #{pr['html_url']} 1>&2")
   system("git config --add pullrequest.id #{pr['number']} 1>&2")
-  system("git config --add pullrequest.branch #{pr['head']['ref']} 1>&2")
+  system("git config --add pullrequest.branch #{branch_ref} 1>&2")
 end
 
 puts JSON.generate(version:  { ref: ref, pr: id.to_s },

spec/integration/in_spec.rb

@@ -57,10 +57,10 @@ def commit(msg)
     get(version: { ref: @ref, pr: '1' }, source: { uri: git_uri, repo: 'jtarchie/test' })
 
     value = git('rev-parse --abbrev-ref HEAD', dest_dir)
-    expect(value).to eq 'pr-1'
+    expect(value).to eq 'foo'
   end
 
-  it 'sets original branch ref' do
+  it 'sets config variable to branch name' do
     get(version: { ref: @ref, pr: '1' }, source: { uri: git_uri, repo: 'jtarchie/test' })
     value = git('config pullrequest.branch', dest_dir)
     expect(value).to eq 'foo'