Correct raw table regex in test_security_groups_rpc

Currently in test_security_groups_rpc, raw table regex uses nat table
chains regex but raw table chains[1] is a strict subset of nat table
chains[2] so a more strict regex should be used as raw table chains
regex.

[1] OUTPUT, PREROUTING
[2] OUTPUT, POSTROUTING, PREROUTING, float-snat, snat

Change-Id: I6f32cda917c2f882f5fd17b6fa105def5572cdef
Merge "Correct raw table regex in test_security_groups_rpc"