Add distribution to drenv metadata

[nirs]

This can be used to do the right thing for ocp or k8s clusters in tests or tools using environment files.

[rakeshgm]

Looks quite useful. What about documenting this env variable.

[nirs]

Looks quite useful. What about documenting this env variable.

Right, need to document it.

[rakeshgm]

my observations are just nits, but on the whole. this looks good to me.