typing imports fail with Python 3.5.0 or 3.5.1

[mattsb42-aws]

Problem

Due to a known bug with Python 3.5.1 and earlier, our use of typing types fail immediately on import in Python 3.5.0 and 3.5.1.

Solution

Add try/catch blocks around the typing imports.

This will allow incompatible Python versions to proceed successfully if they cannot import the requested objects.

Because we use Python 2 style mypy annotations and the only thing that uses the typing imports is the mypy analyzer, the only time that the imported objects are used is when the mypy analyzer runs. As long as we ensure that we do not run the mypy testenvs with either of these versions, this should not be a problem.