Use primary ENI SGs if SG is null for Custom networking

[jayanthvn]

What type of PR is this?
Bug

Which issue does this PR fix:
#1124

What does this PR do / Why do we need it:
If SG is not provided in the ENIConfig then use the primary ENI SGs.

If an issue # is not available please add repro steps and logs from IPAMD/CNI showing the issue:

Testing done on this change:

Created ENI config -

cat <<EOF  | kubectl apply -f -
apiVersion: crd.k8s.amazonaws.com/v1alpha1
kind: ENIConfig
metadata:
 name: $AZ1
spec:
  subnet: $CUST_SNET1
EOF

Before fix SG list is empty-

{"level":"info","ts":"2020-10-12T21:11:32.781Z","caller":"awsutils/awsutils.go:610","msg":"Using a custom network config for the new ENI"}
{"level":"info","ts":"2020-10-12T21:11:32.781Z","caller":"awsutils/awsutils.go:610","msg":"Creating ENI with security groups: [] in subnet: subnet-0ac93d8034479e1cf"}
{"level":"info","ts":"2020-10-12T21:11:33.157Z","caller":"awsutils/awsutils.go:610","msg":"Created a new ENI: eni-014407d03b4c13b5f"}

Terminated the nodes and new nodes after fix -

{"level":"info","ts":"2020-10-12T20:55:44.350Z","caller":"ipamd/ipamd.go:638","msg":"ipamd: using custom network config: [], subnet-0ac93d8034479e1cf"}
{"level":"info","ts":"2020-10-12T20:55:44.350Z","caller":"awsutils/awsutils.go:610","msg":"Using a custom network config for the new ENI"}
{"level":"info","ts":"2020-10-12T20:55:44.350Z","caller":"awsutils/awsutils.go:610","msg":"Creating ENI with security groups: [sg-04b933767a4f1d5a0 sg-0c23b7680a45ebfa0] in subnet: subnet-0ac93d8034479e1cf"}
{"level":"info","ts":"2020-10-12T20:55:44.833Z","caller":"awsutils/awsutils.go:610","msg":"Created a new ENI: eni-04344bd43a8d9af7d"}

Automation added to e2e:

Will this break upgrades or downgrades. Has updating a running cluster been tested?:
Upgrades and downgrades should not be impacted. One thing to call out, eni should be deleted and added back for the change to take into effect like terminating the node. Just upgrade will find the existing ENI and re-use it so SG won't be updated.

Does this change require updates to the CNI daemonset config files to work?:

No

Does this PR introduce any user-facing change?:

No

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

[mogren]

It needs a rebase, but otherwise it looks good.

[nithu0115]

/lgtm. Requesting minor rewording.