Replace deprecated collections.Iterable with abc replacement (SC-127)

[TheRealFalcon]

Proposed Commit Message

Replace deprecated collections.Iterable with abc replacement

LP: #1932048

Additional Context

Deprecated since version 3.3, will be removed in version 3.10: Moved Collections Abstract Base Classes to the collections.abc module. For backwards compatibility, they continue to be visible in this module through Python 3.9.

https://docs.python.org/3.9/library/collections.html

I did a quick search for any other references to something in collections that should be coming from collections.abc and didn't find anything.

Test Steps

n/a

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[blackboxsw]

Approve only python3.5 support needed for collections.abc. No need to support earlier per https://lists.launchpad.net/cloud-init/msg00336.html