test: use our special downloaded dir for 'source' result

Otherwise the test run as root fails seeing the
W: Can't drop privileges for downloading as file 'foo_1.tar.gz' couldn't be
accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
warning in a command which isn't supposed to warn.

One trivial test, two fixups and still counting…

Git-Dch: Ignore

test/integration/test-bug-814139-pickup-of-different-cache-states

@@ -23,11 +23,13 @@ testrun() {
 	testsuccess aptget build-dep foo -y
 	testdpkginstalled 'bar'
 	cleanup
+	cd downloaded
 	testsuccess aptget source foo
 	testsuccess test -s foo_1.tar.* -a -s foo_1.dsc
 	rm foo_1.tar.* foo_1.dsc
 	testsuccess test -d foo-1
 	rm -rf foo-1
+	cd ..
 	cleanup
 	testsuccess aptget install foo -y
 }