Add test for MANAGE_EXTERNAL_STORAGE UI

Adds a unit test for ManageExternalStorageDetails to ensure it calls
AppOpsManager and toggles the preference switch accordingle.

Test: make RunSettingsRoboTests ROBOTEST_FILTER=ManageExternalStorageDetailsTest
Bug: 146425146
Change-Id: Ibd41e189b34c13413b504c101833629cc577b8ac
1 file changed