Avoids relying on external storage and using the hardcoded /sdcard/ path.
Unrooted adb does not have access to non-user 0 sdcard paths, and so the "cp"
command fails when the test runs in user 10.
Fixes: 121400865
Test: cts-tradefed run cts-dev -m CtsNetTestCases -t android.net.cts.NetworkWatchlistTest#testGetWatchlistConfigHash in user 10.
Change-Id: Idc667072bcfbbe159416fa7c7b6b19045b52041d