let valgrind fail when test app returns 0 but valgrind still found an error

this allows to trace uninitialized variables etc with our default
memcheck runs because now valgrind will fail such a test, even though
the test executable returned zero on exit

CTestConfig.cmake

@@ -11,4 +11,4 @@ set(CTEST_DROP_METHOD "http")
 set(CTEST_DROP_SITE "my.cdash.org")
 set(CTEST_DROP_LOCATION "/submit.php?project=srsLTE")
 set(CTEST_DROP_SITE_CDASH TRUE)
-set(VALGRIND_COMMAND_OPTIONS "--trace-children=yes --leak-check=full --show-reachable=yes --vex-guest-max-insns=25")
+set(VALGRIND_COMMAND_OPTIONS "--error-exitcode=1 --trace-children=yes --leak-check=full --show-reachable=yes --vex-guest-max-insns=25")