Fix generation of #line directives in Python 2
Fix generation of #line directives in Python 2

When using Python 2 (which is done in the Makefile), all #line
directives from the test code were generated with the line number 1.
This traces back to the change in the method name for generators in
Python 2 (next) vs Python 3 (__next__). Override both methods so that
the script remains compatible with both Python 2 and Python 3.

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