Bug 1469629 - Read system level policies on Linux if available. r=stransky a=pascalc

  _getConfigurationFile() {

    let configFile = null;

    if (AppConstants.platform == "linux") {

      let systemConfigFile = Cc["@mozilla.org/file/local;1"].createInstance(

        Ci.nsIFile

      );

      systemConfigFile.initWithPath(

        "/etc/" + Services.appinfo.name.toLowerCase() + "/policies"

      );

      systemConfigFile.append(POLICIES_FILENAME);

      if (systemConfigFile.exists()) {

        return systemConfigFile;

      }

    }

    try {

      configFile = Services.dirsvc.get("XREAppDist", Ci.nsIFile);

      configFile.append(POLICIES_FILENAME);