Fix import of collections.Iterable for Python 3.10

[wilsonzlin]

It seems that most Python code in the repo imports Iterable as such:

try:
    from collections.abc import Iterable
except ImportError:
    from collections import Iterable

This commit fixes some imports of Iterable to match this style, and makes them compatible with Python 3.10, which moved Iterable to collections.abc.

[ghost]

All CLA requirements met.