Split build and service environment variables in cloud functions modules

[ludoo]

We always took a shortcut in the CF modules with environment variables, when we used a single variable to define both build and service variables. Now this (which was not entirely ok to start with) generates a permadiff with the introduction of log execution.

We need to change the variable so it has optional build and service members, and default service_config.environment_variables["LOG_EXECUTION_ID"] to avoid a permadiff.