gen_test_desc.py: Improve completion message.

The original messsage said "NNN children to be spawned", which is
confusing when run locally, as nothing is actually spawned by this
script. Replace with mpre neutral "NNN test configurations to be
built".

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I9d7c6545ab51a030fb560096cfd71eb044ddc074
1 file changed