change old failover docs

[andrewh1978]

ahill@ahill--Mac14:~/px-deploy ‹master›$ grep -r "activate migratio" .
./docs/templates/metro/README.md:storkctl activate migration -n petclinic
./docs/templates/async-dr/README.md:storkctl activate migration -n petclinic
./templates/metro.yml:# Scale up on cluster 2 with storkctl activate migration on master-2
./assets/training/archive/Disaster_Recovery/cheatsheet.txt:storkctl activate migration -n postgres