Fix rule duplication with static NAT rules

[richardlawley]

Description

The VR code has provision for inserting rules at the top or bottom by specifying "front" as the second parameter to self.fw.append. However, there are a number of cases where someone has been unaware of this and added a rule with the pattern self.fw.append(["mangle", "", "-I PREROUTING".... This causes the code to check for the rule already being present to fail, and duplicate rules end up being added.

This PR fixes two of these cases which apply to adding static NAT rules. I am aware of more of these cases, but I don't have the ability to easily test the outcome of fixing them. I'm happy to add these in if you're confident that the automated tests will be sufficient. Searching for "-I (case sensitive) finds these.

The code for dealing with "front" is included below to show that this shouldn't have any ill effects:

if fw[1] == "front":
cpy = cpy.replace('-A', '-I')

Fixes: #3177

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)

How Has This Been Tested?

Local tests were performed (see #3177 for details of symptoms), and we have had this fix deployed in production on advanced networks for a couple of months.

[yadvr]

Can you review this - @ustcweizhou@anuragaw@shwstppr ?
@blueorangutan package

[blueorangutan]

@rhtyd a Jenkins job has been kicked to build packages. I'll keep you posted as I make progress.

[yadvr]

Thanks for the PR @richardlawley - do you think it can cause regression when the VR has multiple public IPs (i.e multiple public nics) as this reverts changes from 40d7746

[yadvr]

Nevermind I compared your changes with what Jayapal was trying to do, LGTM.

[blueorangutan]

Packaging result: ✔centos6 ✔centos7 ✔debian. JID-2838

[yadvr]

@blueorangutan test

[blueorangutan]

@rhtyd a Trillian-Jenkins test job (centos7 mgmt + kvm-centos7) has been kicked to run smoke tests

[blueorangutan]

Trillian test result (tid-3641)
Environment: kvm-centos7 (x2), Advanced Networking with Mgmt server 7
Total time taken: 29513 seconds
Marvin logs: https://github.com/blueorangutan/acs-prs/releases/download/trillian/pr3366-t3641-kvm-centos7.zip
Smoke tests completed. 69 look OK, 0 have error(s)
Only failed tests results shown below:

Test	Result	Time (s)	Test File

[ustcweizhou]

I was just testing it. it works fine.