Fix 2.10.x branch for Python 3.12 and beyond

[rahulrajaram]

NOTICE: Prior to submitting a pull request, please ensure you abide by the
Guidelines for Code Contributions, including but not limited to:

• PR is associated with at least one issue: Failure on 2.10.x branch using Python 3.12 #672
• Submit from a topic branch, not a pre-existing Cement branch: Fix210xBranchForPython312
• Make every effort to comply with PEP8
• All tests pass successfully: Yes. I did not add any new tests since the existing tests suffice.
• Coverage reports 100% code coverage: Since I've added a conditional check for Python version < 3.4 in ext_plugin.py coverage of this file has fallen to 93%. I'm open to suggestions.

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Issue: #672

[derks]

@rahulrajaram thank you for the PR. Cement 2.x is very old... Travis tests all fail simply because it was setup to test against older versions of Python (2.7, <3.5). I understand moving to Cement 3.x may not be possible right away however I wanted to stress that Cement 2.x has been unofficially EOL for years and should be moved away from as soon as possible for anything under active development/use.

I am OK with merging this in as long as it doesn't break anything.... but I need to put some work into updating the dev environment for testing.

[rahulrajaram]

@derks , thanks for your response and clarifying the status of Cement 2.x.

I could take a stab at fixing the dev setup, but could you clarify what versions of Python you intend on supporting with the 2.10.x series. Although I am able to get the tests to pass with 3.7 and 3.12, I am not able to get them to pass with 3.5 because the latest versions of certain cement dependencies won't build. Would you be okay dropping support from Python < 3.7?