native test: End tests as soon as they pass fail

To avoid indeterministic behaviour of the tests
which leads to changing coverage reports, let's
finish the tests exectuion as soon as they pass
or fail.
Also let's return 0 to the shell if the test passed,
and 1 if it failed.

(Reverting
f9af42f078c93eca8b9f461f91b6cafddb57a35d and
07c9163f
)

Signed-off-by: Alberto Escolar Piedras <alpi@oticon.com>