Pytest includes a fixture that can be used to generate temporary
directories. Previously Pegleg had implemented a hombrewed version of a
temporary directory fixture. This change removes the homebrewed version
and replaces it with the tmpdir fixture.
Implement tmpdir fixture in tests
Upgrade all testing packages to use the latest features
Removes unused imports and organizes import lists
Removes mock package requirement and uses unittest.mock, included in
python >3.3
Implements a slightly cleaner method to get proxy info
Change-Id: If66e1cfba858d5fb8948529deb8fb2d32345f630
4480ab5574