Feature/environments

[adrienbernede]

Updates #18.

Missing:

• testing this, of course
• force re-concretization. Either with spack concretize -f, or by removing the spack.lock. Most likely the latter.
• pass new mirror to the environment with spack command instead of config edit.
• copy environment in the uberenv_libs location to modify at will (see previous action).

The methodology here is to start with an empty environment: no spec.
Then uberenv adds the selected spec to the environment.

[cyrush]

The logic to setup the env is much simpler than the current patching which is nice.

I hope we can keep the current logic and have an independent path for the env case.

We can select the env path by the existence of a spack.yaml file, vs compilers.yaml etc, or better create a command line option --spack-env that takes the spack.yaml file directly. Other than the env setup being different, I think the only other thing needed is to use -e . during the spack install steps. Also important is understanding how python packages are activated in the env case, I haven't look at that at all yet.

Concretely: We should keep patch and add a case for the env logic.

On the other TODOS / Questions:

We should keep the print of the spack python info. I have hit a few cases where folks were very confused by spack using a different python than uberenv was, that print helps us sort out cases like that.

I also think we should keep the hot copy feature for the packages.

[adrienbernede]

LGTM