fix(manager-installation): using correct paramter for GCE region
fix(manager-installation): using correct paramter for GCE region

Fixes exception:    region = self.params.get('region_name').split()
AttributeError: 'NoneType' object has no attribute 'split'

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