ADD: unstable env for users

env/sles15/x86_64/users/unstable/spack.yaml

@@ -0,0 +1,19 @@
+spack:
+  concretizer:
+    unify: false
+  config:
+    allow_sgid: false
+    build_stage:
+      - $spack/user/$user/spack-stage
+    install_tree:
+      root: $spack/user/$user/spack-install
+    upstreams:
+      spack-instance-1:
+        install_tree: $spack/opt/spack/stable
+      spack-instance-2:
+        install_tree: $spack/opt/spack/unstable
+    include:
+    - $spack/spack-psi/env/$os/$target_family/sysconfigs/packages.yaml
+    - $spack/spack-psi/env/$os/$target_family/sysconfigs/compilers.yaml
+    specs:
+  view: false