Adding e2e focus and skip for sonobuoy as flags.

[haouc]

Issue #, if available:

Description of changes:
If we need run upstream conformance test against to specific groups, we need add focus or skip as flags for sonobuoy.

Tests

{"msg":"Test Suite completed","total":32,"completed":32,"skipped":5635,"failed":0}

Ran 32 of 5667 Specs in 468.099 seconds
SUCCESS! -- 32 Passed | 0 Failed | 0 Pending | 5635 Skipped
PASS

Focus on sig-network tests

AWS_K8S_TESTER_EKS_ADD_ON_CONFORMANCE_SONOBUOY_E2E_FOCUS="sig-network.*\[Conformance\]"
sonobuoy-e2e-focus: sig-network.*\[Conformance\]
  sonobuoy-e2e-repo-config: ""
  sonobuoy-e2e-skip: ""

Plugin: e2e
Status: passed
Total: 5667
Passed: 32
Failed: 0
Skipped: 5635

Plugin: systemd-logs
Status: passed
Total: 5
Passed: 5
Failed: 0
Skipped: 0

*********************************************************
General tests

AWS_K8S_TESTER_EKS_ADD_ON_CONFORMANCE_ENABLE=true

Plugin: e2e
Status: passed
Total: 5667
Passed: 311
Failed: 0
Skipped: 5356

Plugin: systemd-logs
Status: passed
Total: 5
Passed: 5
Failed: 0
Skipped: 0

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