Add new KubectlClient.exec_bg helper

[HashNuke]

Issues:

Refs: cncf/cnf-testsuite#1738

Description

These changes help with resolving compile issues mentioned in cncf/cnf-testsuite#1738

• Removes background arg from KubectlClient.exec. This caused errors due to unexpected return value when used in the testsuite.
• Adds new helper KubectlClient.exec_bg for executing in the background. This should help any ongoing work in other branches and behaves the same as the earlier exec helper with background=true.

Additional changes to help smooth transition for cncf/cnf-testsuite#1726

• Add deprecated helper functions with old signatures as per usage in main branch in cncf/cnf-testsuite.
• This ensures that the main branch of kubectl_client works with the cnf-testsuite when compiled.
• These changes have been tested with a fork of the main branch of cncf/cnf-testsuite
  • Branch name: bug/1738
  • Build link: https://github.com/cncf/cnf-testsuite/actions/runs/4174668958

More notes

For validation against the main branch of cnf-testsuite: This exec-background branch of kubectl_client is now being used by the bug/1726 branch of cncf/cnf-testsuite and the build is green.

How has this been tested:

• Covered by existing integration testing
• Added integration testing to cover
• Verified all A/C passes
  • develop
  • master
  • tag/other branch
• Test environment
  • Shared Packet K8s cluster
  • New Packet K8s cluster
  • Kind cluster
• Have not tested

Types of changes:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

Documentation

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• No updates required.

Code Review

• Does the test handle fatal exceptions, ie. rescue block

Issue

• Tasks in issue are checked off

[agentpoyo]

LGTM