As the number of ports per default security group increases, the
number of iptables entries on the Compute Node grows. Because of
this, there is a gradual increase in the time taken to apply chains
and rules.
Currently we are using list comprehensions to find if a new chain or
rule matches an existing one. Instead, walk through the list in
reverse to find a matching entry.
Added a new method, _find_last_entry(), to return the entry we are
searching for.
Change-Id: I3585479ffa00be556b8b21dc9dbd6b36ad37f4de
Closes-Bug: #1302272
Related-Bug: #1253993
2175c85d83