[meta] fail make test on error

[jmlrt]

This commit fix the make test target to fail with the proper exit code
if a shell command is failing.

Fix #1385

[jmlrt]

CI tests are expected to fail because of #1375

[jmlrt]

Reproduced with a test Makefile:

• This is successful despite ls $TEST_VAR is failing:

$ make -f test.mk
for i in $(seq 1 5); do \
                if [ -z "$TEST_VAR" ]; then \
                        sleep 1; \
                        echo "waiting"; \
                        TEST_VAR=toto; \
                else \
                        echo "Testing: $TEST_VAR" && \
                        ls $TEST_VAR; \
                        break; \
                fi; \
        done
waiting
Testing: toto
ls: toto: No such file or directory
$ echo $?
0

• This is failing as expected:

$ make -f test.mk
set -eo pipefail; \
        for i in $(seq 1 5); do \
                if [ -z "$TEST_VAR" ]; then \
                        sleep 1; \
                        echo "waiting"; \
                        TEST_VAR=toto; \
                else \
                        echo "Testing: $TEST_VAR" && \
                        ls $TEST_VAR; \
                        break; \
                fi; \
        done
waiting
Testing: toto
ls: toto: No such file or directory
make: *** [test] Error 1
$ echo $?        
2

[Conky5]

LGTM