Do reset the env values when --reset is used

When I use `vmc push --reset` with a manifest I noticed that the environment variables were not re-applied as defined in the manifest.

This patch does apply the environment variables as defined in the manifest with a `vmc push --reset`.

I am aware that there is no active development on the vmc related repositories.
Let me know if the change of behaviour makes sense, I'll port it the patch to manifests-cf-plugin and add some tests.
Otherwise I would certainly like to know if there is a command that would `vmc reset-env --manifest manifest.yml` ?

Thanks for your attention.