Otadexopt: Expose progress percentage

To be able to report progress of an A/B OTA dexopt, expose a
progress function that the script can query.

Bug: 25612095
Bug: 29223204
Change-Id: Ie8162946d18f6fa78649a40ad5d3949d31a181cd
(cherry picked from commit bf06232f4d440ced8230662a77ca0e8ece6383ca)
3 files changed