fix(longevity-pipeline): do not run provision resources stage on non-AWS
fix(longevity-pipeline): do not run provision resources stage on non-AWS

Recently was added "provision resources" stage to the 'longevity'
pipeline. This stage silently fails if we use any non-AWS backend.
In such a case stage gets marked as 'SUCCESS', but silently marks
whole build as "FAILURE".

So, check the backend explicitely and skip this step completely avoiding
false negative results using non-supported backends.

Also, update post actions with more info about completed stages for
better visibility.

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests