fix: ignore errors when vpc does not have default security groups

[michaelhtm]

Issue #2661

Description of changes:
Currently the controller has been returning an error if the VPC
securityGroup is not found. With this change, we will ignore errors if
we can't find the security group

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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This pull-request has been approved by: michaelhtm

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@michaelhtm: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ec2-verify-code-gen	887d501	link	false	/test ec2-verify-code-gen

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