Reload iptables after purging rules, add rsyslog to post_start_hooks

In some cases, rsyslog would only unmasquerade UDP connections
and not TCP connections, causing issues with deployment.

This commit includes fixes for purging old iptables
rules that run into race conditions, as well as a fix
for grep to include '--' to handle strings that
start with dash.

Change-Id: I3913cb2ebd7fee42039e280f676b80f8f36e1841
Closes-Bug: #1360298
Merge "Reload iptables after purging rules, add rsyslog to post_start_hooks"