message: Fix error while opening blackfire configuration file on Linux
diff: add_blackfire_linux() {
  - sudo mkdir -p /var/run/blackfire
  + sudo mkdir -p /var/run/blackfire /etc/blackfire
  add_list debian/blackfire http://packages.blackfire.io/debian https://packages.blackfire.io/gpg.key any main
  install_packages blackfire
  + sudo chmod 777 /etc/blackfire/agent
  }
  add_blackfire_darwin() {
  