Use spack bootstrap now to find clingo

[chapman39]

Use spack commands to setup clingo rather than relying on pip. Currently, this is only being tested in dev-build CI jobs.

Ready for review and discussion.

Fixes #118

[chapman39]

Should clingo be the default concretizer in uberenv?

[chapman39]

[exe: /home/runner/work/uberenv/uberenv/.ci/test-project/uberenv_libs/spack/bin/spack bootstrap now]
==> Fetching https://mirror.spack.io/bootstrap/github-actions/v0.4/build_cache/linux-centos7-x86_64-gcc-10.2.1-clingo-bootstrap-spack-idkenmhnscjlu5gjqhpcqa4h7o2a7aow.spec.json
==> Fetching https://mirror.spack.io/bootstrap/github-actions/v0.4/build_cache/linux-centos7-x86_[64](https://github.com/LLNL/uberenv/actions/runs/6030953662/job/16363766980?pr=122#step:4:65)/gcc-10.2.1/clingo-bootstrap-spack/linux-centos7-x86_64-gcc-10.2.1-clingo-bootstrap-spack-idkenmhnscjlu5gjqhpcqa4h7o2a7aow.spack
==> Installing "clingo-bootstrap@=spack%gcc@=10.2.1~docs~ipo+python+static_libstdcpp build_type=Release arch=linux-centos7-x86_64" from a buildcache
[exe: /home/runner/work/uberenv/uberenv/.ci/test-project/uberenv_libs/spack/bin/spack bootstrap status]
Spack v0.21.0.dev0 - [email protected]

[PASS] Core Functionalities

[PASS] Binary packages

https://github.com/LLNL/uberenv/actions/runs/6030953662/job/16363766980?pr=122#step:4:66