Add TmpDir, PushPopD context managers.
Add TmpDir, PushPopD context managers.

TmpDir creates a temporary directory when entering, and removes it and
its contents when exiting the context.

PushPopD changes into a directory when entering, and back into the
previous one when exiting the context.

Signed-off-by: Nils Philippsen <ad3fa8d847df2b57853a376ad688e4be8041ecd4@redhat.com>

fedora-infra/pdc-updater