Move reading BUILDENV_HOST_IP variable to the job script definition

[0xnm]

What does this PR do?

We've changed the runner type here #1789 and since it is now k8s-based, the variables that depends on information related to k8s resources (host IP) needs to be referenced directly from the job otherwise is not going to work.

This PR fixes dd-trace-java bootstrap which was failing, because BUILDENV_HOST_IP wasn't available at the variables set stage.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

Merging #1801 (4c92f31) into develop (12d25e5) will increase coverage by 0.11%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1801      +/-   ##
===========================================
+ Coverage    83.41%   83.51%   +0.11%     
===========================================
  Files          466      466              
  Lines        16371    16348      -23     
  Branches      2453     2454       +1     
===========================================
- Hits         13655    13653       -2     
+ Misses        2041     2031      -10     
+ Partials       675      664      -11     

see 20 files with indirect coverage changes