Don't use /tmp on Windows, instead use value of TEMP env variable.

Also give an error if no appropriate environment variables are set.
Add InitializeWindows() call to avoid crash popups on Windows.

Popups block the test execution.
Rename mock-package-manager to use '_' for easier tool handling.

Main reason is that '-' is not allowed in variable names.

Redmine #5266.
Several Windows fixes regarding shell rules and path separators.
Skip some test cases on Windows.

Those that test package listing functionality directly are marked as
unsupported, since Windows doesn't use the package body for that.
Those that merely depend on it for testing something else are marked
as needs_work.
Merge pull request #1634 from kacfengine/mock-package-manager_win

Redmine #5266: Package test fixes for Windows