Print a command trace if the check-names.sh exits unexpectedly
Print a command trace if the check-names.sh exits unexpectedly

We've observed that sometimes check-names.sh exits unexpectedly with
status 2 and no error message. The failure is not reproducible. This
commits makes the script print a trace if it exits unexpectedly.

ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls