(PUP-2943) Add PMT --ignore-changes

Prior to this commit there was no way to only ignore local changes to a module.
You had to --force when upgrading/uninstalling, which could potentially have other
repurcussions.
This commit adds the --ignore-changes flag, so a user can specify that they don't
care about local file changes but do not want to force anything else.
(PUP-2943) Uninstall/upgrade ignore changes spec

Adding more spec tests for the --ignore-changes flag on uninstall/upgrade
(PUP-2943) Clean ignore-changes uninstall logic
(PUP-2943) Update acceptance tests

Update wording to reflect --ignore-changes flag suggestion instead of --force.
Merge pull request #2899 from highb/fix/stable/pup-2943_ignore_changes_flag

(PUP-2943) Add PMT --ignore-changes flag