Improve the fallout performance test procedure

After is done, we have the performance testing procedure for java driver OSS in the repository.
The procedure can be improved in this ticket:

• we should investigate if it is possible to merge two separate YAML files (One is for the setup of an observer with grafana. Second is for actual performance tests). It should be feasible to merge them into one file. Once it will be in one file we will remove one manual step of copying observer IP into graphite_host: {provide-graphite-host-ip}

• The fallout procedure still users variables for DSE (like for example dse.git.branch: driver_dse_branch)
  We should investigate if they are needed and remove them if possible from OSS plan.

• the run-endurance step is duplicated in both: graphite-setup.yaml and oss-performance-setup.yaml.
  It seems that this stage in graphite-setup.yaml is not needed