[Issue 1176] Fix uptimer setup

[jochenehret]

WHAT is this change about?

• don't run the upgrade jobs two times as the second attempt is a BOSH no-op and will not measure anything meaningful
• configure stats check threshold (see feat: App stats availability measurement uptimer#115)

What customer problem is being addressed? Use customer persona to define the problem e.g. Alana is unable to...

Alana wants to have a downtime validation when upgrading the cf-deployment version.

Please provide any contextual information.

#1176

Has a cf-deployment including this change passed cf-acceptance-tests?

N/A

Does this PR introduce a breaking change? Please take a moment to read through the examples before answering the question.

• YES - please choose the category from below. Feel free to provide additional details.
• NO

How should this change be described in cf-deployment release notes?

N/A

Does this PR introduce a new BOSH release into the base cf-deployment.yml manifest or any ops-files?

• YES - please specify
• NO

Does this PR make a change to an experimental or GA'd feature/component?

• experimental feature/component
• GA'd feature/component

Please provide Acceptance Criteria for this change?

The "bosh-deploy-cf-develop" tasks in the "upgrade-deploy" and "experimental-deploy" jobs are green and produce meaningful uptimer reports.

What is the level of urgency for publishing this change?

• Urgent - unblocks current or future work
• Slightly Less than Urgent