Fix/issue 802 - FW routes

[fredbonin]

I only add the suffix for the second route created so that it does not break current installation. See comment below :

    // Since we want to continue to support old installation, we only add the suffix for the second routes and onward since
    // they probably don't exist (see https://github.com/aws-samples/aws-secure-environment-accelerator/issues/802)
    // If we fixed the bug for all routes, the stack would fail on first run because it would try to create the
    // new route without deleting the old one first and it is not possible to have multiple routes with the same destination

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