Fetches a list of open changes that have not been updated since a
given age (default 6 months), and then abandons them.
Assumes that the user's credentials are in the .netrc file. Supports
either basic or digest authentication.
Example to abandon changes that have not been updated for 3 years:
./abandon_stale --gerrit-url http://review.example.com/ --age 3years
Supports dry-run mode to only list the stale changes but not actually
abandon them.
Requires pygerrit (https://github.com/sonyxperiadev/pygerrit).
Change-Id: Ie0edb54847f9f2ab8204647e17e3893ed0a057ea
