added checks for iptables return status (https://github.com/globaleaks/GlobaLeaks/issues/291)
added checks for iptables return status (https://github.com/globaleaks/GlobaLeaks/issues/291)

vodkina/GlobaLeaks,vodkina/GlobaLeaks,vodkina/GlobaLeaks,vodkina/GlobaLeaks