Update site probabilities for PRG trial

[stephen-soltesz]

This change adjusts the site probabilities of PRG and regional cloud sites to direct more traffic to regional locations outside of PRG.

This change additionally restores the --no-promote flag for production deployments due to #114

Part of:

• https://github.com/m-lab/ops-tracker/issues/1720

---

This change is 

[coveralls]

Pull Request Test Coverage Report for Build 799

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.333%

---

Totals
Change from base Build 796:	0.0%
Covered Lines:	1576
Relevant Lines:	1636

---

💛 - Coveralls

[nkinkade]

, with one small question.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @stephen-soltesz)

---

cloudbuild/cloudbuild.yaml line 51 at r1 (raw file):

    -e 's/{{REDIS_ADDRESS}}/$_REDIS_ADDRESS/'
    app.yaml
  - gcloud --project $PROJECT_ID app deploy --no-promote app.yaml

Just checking that this should in fact be --no-promote

[stephen-soltesz]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @nkinkade)

---

cloudbuild/cloudbuild.yaml line 51 at r1 (raw file):

Previously, nkinkade wrote…

Just checking that this should in fact be --no-promote

Yes, without --no-promote the deployment disrupts continuity of service - see the image in #114

With this change we will have to manually promote the new version gradually, but we should be able to create a tool to do this for us shortly.