Switch formatElapsedTime to use ICU's MeasureFormat

Previously, localizable strings were used instead, causing various
difficulties and inconsistencies. The formatting code also
hard-coded the pluralization rules for English and used it for all
locales.

Now we use ICU's MeasureFormat. There are some small formatting
differences with the previous code, but they are not important,
especially since the old strings were not necessarily well-thought.

Bug: 36994779
Test: adb shell am instrument -w -e package android.text com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Change-Id: Ie8cb119a76e89e2ee971353761fbd54e0d9a556c