Use standalone pipeline for e2e
The following changes are made as part of this PR
- Scripts to pull and install opTestrunner, gecco and gtgen binaries
- Script to build gtgen directly on CI incase the binary is not available
- Update dockerfile to support the current changes
- Use jenkinsfile.e2e file to run a seperate pipeline for e2e tests
- Update Jenkinsfile which now acts as a pipeline for umbrella repository