Fix exception handling in serverless startup script. (#545)
Fix exception handling in serverless startup script. (#545)

The script was catching the wrong exception class (ValueError instead
of KeyError), but this new approach is easier to read anyway.
cloudendpoints/esp,cloudendpoints/esp,cloudendpoints/esp,cloudendpoints/esp,cloudendpoints/esp,cloudendpoints/esp,cloudendpoints/esp,cloudendpoints/esp