Missing type validation

[ghost]

Although type hints are used throughout the package, there doesn't seem to be any type validation being done.

Running mypy for the podman package currently returns quite a few type errors:

$ mypy --package podman
...
Found 152 errors in 22 files (checked 74 source files)

The number of errors will be bigger or smaller depending on the mypy config that is used. Also, specific lines/modules can be ignored if they shouldn't be checked. Lastly, perhaps mypy is not the type checking tool that is to be used.

[umohnani8]

Duplicate of #293, closing in favor of that one.