Pushing to Docker-Hub is triggerd by timmer and not content

[uCatu]

Pushing on daily timmer is creating overhead and confusion image timestamp is updated without any phsyical channge.

conjur-base-image/Jenkinsfile

Line 70 in bee5eec

triggeredBy 'TimerTrigger'

Suggestio:

• trigge by tag which is a manual action that developer need to remeber
  when { buildingTag() }

Or

• trigger by SCM SHA code change detection, completely automatic, but can cause commits the be public as soon as push instead of aggregated into version.

• Need to investigate behavior on Jenkins build replay or just triggering build and when we do git rebase

[sashaCher]

I guess that the decision of to push to DockerHub or not to push should be a function of the next inputs:
One of the Dockerfiles of build.sh scripts has changed from the last time triggered build
or
Base Ubuntu or Phusion image has been updated from the last time triggered build

The first one will validate that we're pushing only when valuable changes have been made in image build content/process.
The second one will validate that we're up to date with latests Ubuntu/Phusion changes and do not miss any security upgrade.

In addition we should publish date tag. It will allow to roll back to specific date tag in case and we harm latest.

[uCatu]

@sashaCher There is a caveat that we need to pay attention to - If we will push on changes (Dockerfiles or Base iamge) we leave no time to check master correctness before release. Some feature might require us to accumulate commits before releaseing