Add universal check of env vars in cmind.utils

[Grigori Fursin]

We have lots of following code in CM scripts:

    if str(env.get('CM_DOCKER_PUSH_IMAGE', '')).lower() in ['true', 'yes', 'on']:

I suggest to provide a cmind.utils.is_env_true and cmind.utils.is_env_false` to unify it ...
We will then need to add an extra check for min CM versions in such updated scripts: mlcommons/cm4mlops#15

[Admin account for cTuning.org]

Done.