Summary:
When KWin successfully presents a new mode, it stores the current state
as the last working mode. If a new modeset is requested and the atomic
test fails, all is undone and reverted to this last knowing mode.

Currently included are:
 * the mode
 * global position
 * transformation

This is only done on a modeset not when going to DPMS.

Test Plan:
Selected the not working vertical rotation and nothing bad
happened.

Reviewers: #kwin, #plasma, subdiff

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D8602