Make showing percentage texts configurable on shutdown dialog

Bug: 315235777
Test: Made a patch so the shutdown to update dialog screen would show up on each reboot, and stay there for some time.
(cherry picked from https://partner-android-review.googlesource.com/q/commit:f6fa76c6e6ec825e4da9508f8a018fc1408558ca)
Merged-In: I8a60596748fa3d1a4fbea7c115d52fba3a740c75
Change-Id: I8a60596748fa3d1a4fbea7c115d52fba3a740c75