Add READ_EXTERNAL_STORAGE permission to android.content.cts

The test package in question reads wallpaper imagery in several
test cases, an operation which now requires an additional
permission.

bug: 64003109
Test: run cts-dev -m CtsContentTestCases
Change-Id: Ib0abf6d58a340a28774a68b191b9592bfc56044e
1 file changed