spack config get/blame: with no args, show entire config

This PR changes the default behavior of `spack config get` and `spack config blame`
to print a flattened version of the entire spack configuration, including any active 
environment, if the commands are invoked with no section arguments.

The new behavior is used in Gitlab CI to help debug CI configuration, but it can also
be useful when asking for more information in issues, or when simply debugging Spack.

share/spack/gitlab/cloud_pipelines/.gitlab-ci.yml

@@ -150,6 +150,13 @@ default:
     - spack python -c "import os,sys; print(os.path.expandvars(sys.stdin.read()))"
       < "${SPACK_CI_CONFIG_ROOT}/${PIPELINE_MIRROR_TEMPLATE}" > "${SPACK_CI_CONFIG_ROOT}/mirrors.yaml"
     - spack config add -f "${SPACK_CI_CONFIG_ROOT}/mirrors.yaml"
+    - mkdir -p "${CI_PROJECT_DIR}/jobs_scratch_dir"
+    - spack
+      --config-scope "${SPACK_CI_CONFIG_ROOT}"
+      --config-scope "${SPACK_CI_CONFIG_ROOT}/${SPACK_TARGET_PLATFORM}"
+      --config-scope "${SPACK_CI_CONFIG_ROOT}/${SPACK_TARGET_PLATFORM}/${SPACK_TARGET_ARCH}"
+      ${CI_STACK_CONFIG_SCOPES}
+      config blame > "${CI_PROJECT_DIR}/jobs_scratch_dir/spack.yaml.blame"
     - spack -v  --color=always
       --config-scope "${SPACK_CI_CONFIG_ROOT}"
       --config-scope "${SPACK_CI_CONFIG_ROOT}/${SPACK_TARGET_PLATFORM}"