Replace gitreceive by a git plugin.

This removes the need for two distinct users.
Git pushes and dokku commands are sent using the same user.

tests/run_ec2

@@ -36,7 +36,6 @@ set -e
 echo "-----> Connecting and running bootstrap script..."
 cat ../bootstrap.sh | ssh -o "StrictHostKeyChecking=no" ubuntu@$PUBLIC_IP "HOSTNAME=$PUBLIC_IP sudo bash" 2>&1 | indent
 echo "-----> Installing SSH public keys..."
-cat ~/.ssh/id_rsa.pub | ssh -o "StrictHostKeyChecking=no" ubuntu@$PUBLIC_IP "sudo gitreceive upload-key test" > /dev/null
 cat ~/.ssh/id_rsa.pub | ssh -o "StrictHostKeyChecking=no" ubuntu@$PUBLIC_IP "sudo sshcommand acl-add dokku test" > /dev/null
 for app_path in apps/*; do
   app=$(basename $app_path)