script, test:  do not indicate test fails in exit status

Return 0 also if some tests failed, as long as all tests could be run.

Fails are already indicated by echoing <test>.diff.

Change-Id: Ie80e226d8c435527b0fb277e8d556a370a9fc43d
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>