post_test.sh.cmake: Ignore return value of commands

The post test script ensures that all device servers are properly
shutdown.

This sometimes fails on travis with debian buster.

As this is not a relevant part of the test anyway we can just return
with zero exit code.

Author: t-b

cpp_test_suite/environment/post_test.sh.cmake

@@ -7,3 +7,5 @@ kill $PID
 
 PID=$(<@PROJECT_BINARY_DIR@/cpp_test_ds/fwd_ds/FwdTest_@INST_NAME@.pid)
 kill $PID
+
+exit 0