Since FUNCNAME is not defined when running outside a function,
trap does not work and display wrong error message.
Example from https://circleci.com/gh/hashicorp/consul/69506 :
```
⨯ FAIL
/home/circleci/project/test/integration/connect/envoy/run-tests.sh: line 1: FUNCNAME[0]: unbound variable
make: *** [GNUmakefile:363: test-envoy-integ] Error 1
```
This fix will avoid this error message and display the real cause.