Changes

test-topology.sh: use . instead of source
For some reason, autoconf may use /bin/sh for @BASH@
(when /bin/sh points to /bin/bash). It seems to cause some 
incompatibilies on RHEL8 when using "source". Use "." instead.
Thanks to Erik Hamera for the report.
Fixes #369
(even if things aren't clear to me).
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
(cherry picked from commit 6c233212824755d60a388e0e9588ef72a7f7dd8c)