* fix: backport #15030 to fix#14958 dbus crash
* chore: re-enable power spec tests
* chore: undo changes made to power monitor tests.
The Linux failures on that are gone in master / 4-0-x. Whatever
resolved it there is unrelated to this PR's changes, so I'm not
going to block this fix on an unrelated issue.
The event is emitted when the OS is rebooting/shutting down, and allows
an electron app to call `e.preventDefault()` in order to delay shutdown
and exit cleanly.
