Exclude docker from the admin net masquerading

We should exclude -s docker0 form the nailgun iptables
rule for admin network masquerading in order to
elliminate the potential issues related with race condition
during master node deployment.

Closes-bug: #1332517

Change-Id: I942da109d83cce65880a3f27cb1d5301d300da50
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
Merge "Exclude docker from the admin net masquerading"