Do not use global before_scripts in auto devops to increase customizability
## Summary
Auto devops deploy script is currently using global [before_script](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/ci/templates/Jobs/Deploy.gitlab-ci.yml#L569). When using the folling ci file
```
before_script:
- echo hello
include:
- template: Auto-DevOps.gitlab-ci.yml
```
`before_script` of the deploy step is overriden, breaking the entire pipeline.
The before script could be moved in the stages
## Improvements
Global `before_script` wouldn't be cluttered. Extensibility and customizability would increase.
## Risks
-
## Involved components
https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/ci/templates/Jobs/Deploy.gitlab-ci.yml
## Optional: Intended side effects
## Optional: Missing test coverage
issue