volatile-test: Fix purge flag bug

This patch from Minchan fixes a bug with the purge flag
logic, where we end up overwriting the purge value with
whatever the last call returns. Instead we should OR
the results together to see if any data was purged.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Makefile: Integrate fetching/building of external tests into the Makefile

Integrates the fetch-external-tests.sh into Makefile.

Also renames the test file to be more explicit

Signed-off-by: John Stultz <john.stultz@linaro.org>
Rename setup-vrange-anon.sh to fetch-external-tests.sh

Since the script fetches and builds external tests
like ebizzy and jemalloc, reanme it appropriately

Signed-off-by: John Stultz <john.stultz@linaro.org>