Use shorter names for CI clusters (#415)

* use run_number as a shorter ID for CI

* slurmci group name warning

* Revert "slurmci group name warning"  - underscores not valid linux hostname and stripped in host, leading to slurmdbd config failure

This reverts commit 61dfad6.

---------

Co-authored-by: Bertie <bertie@stackhpc.com>

Author: sjpb

.github/workflows/stackhpc.yml

@@ -34,7 +34,7 @@ jobs:
     env:
       ANSIBLE_FORCE_COLOR: True
       OS_CLOUD: openstack
-      TF_VAR_cluster_name: slurmci-${{ matrix.os_version }}-${{ github.run_id }}
+      TF_VAR_cluster_name: slurmci-${{ matrix.os_version }}-${{ github.run_number }}
       CI_CLOUD: ${{ vars.CI_CLOUD }}
     steps:
       - uses: actions/checkout@v2