openssh_cert - cleanup and diff support

[Ajpantuso]

SUMMARY

Significant cleanup of openssh_cert with added diff support;

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

plugins/modules/openssh_cert.py

ADDITIONAL INFORMATION

Changes:

• Added diff support after integration of OpensshCertificate from module_utils
• Refactored integration tests and enabled assertions so that idempotency is always checked. (Also added test cases for known idempotency issues to be addressed in a future PR)
• Time parameters presented in the "validity string" for the -V option will now just use always and forever for arbitrarily large and small dates rather than datetime.min and datetime.max from Python. (No effect to end users as ssh-keygen will behave the same way as when provided out-of-range dates)

Fixes:

• Used AnsibleModule methods to more consistently setup temp files and preserve permissions.
• Ensured backup is taken before final move operation to restore if necessary.

[felixfontein]

Looks good, thanks a lot for working on this!

[felixfontein]

@Ajpantuso thanks for implementing this!

[Ajpantuso]

@Ajpantuso thanks for implementing this!

Thanks for reviewing. The follow-up PR's should be much smaller.