Don't use framework strings for formatting file sizes

Modify various formatters to avoid using framework strings for
formatting file sizes.

Also update README instructions for running unit tests.

Bug: 36994779
Test: adb shell am instrument -w -e class com.android.settings.utils.FileSizeFormatterTest com.android.settings.tests.unit/android.support.test.runner.AndroidJUnitRunner
Test: make -j RunSettingsRoboTests
Change-Id: I4035f26d29408b64389892a4a2379b4823f8ac96
11 files changed