PackageManager : Log stats about the optimizing apps dialog.

Logs the following parameters :
- Total time spent optimizing apps.
- Total number of apps that were dexopted.

TESTED: with adb logcat -b events:
05-04 15:24:16.303  2065  2065 I sysui_action: [402,3]
05-04 15:24:16.303  2065  2065 I sysui_action: [403,34]
05-04 15:24:16.303  2065  2065 I sysui_action: [404,0]
05-04 15:24:16.304  2065  2065 I sysui_action: [405,163]
05-04 15:24:16.304  2065  2065 I sysui_action: [406,12168]

This shows that:
 - 3 apps were optimized
 - 34 apps were skipped
 - 0 apps failed to optimize
 - dialog showed a total of 37 (3 + 34 + 0) apps
 - system has 163 optimizable packages
 - a total of 12.2 seconds was spent in the optimizing apps dialog

bug: 28528058
bug: 28544474
Change-Id: I9eb5229a1589ca0df57d3fc03102992fa90a877f