Trim hostname

[felixbarny]

Context: the output of uname -u may contain a line break. See also https://github.com/elastic/apm-agent-java/pull/2286#issuecomment-979217502

• [x] Create PR as draft
• [ ] Approval by at least one other agent
• [ ] Mark as Ready for Review (automatically requests reviews from all agents and PM via CODEOWNERS)
  • Remove PM from reviewers if impact on product is negligible
  • Remove agents from reviewers if the change is not relevant for them
• [ ] Merge after 2 business days passed without objections

[apmmachine]

:green_heart: Build Succeeded

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#### Build stats * Start Time: 2021-11-29T17:45:57.368+0000 * Duration: 3 min 12 sec * Commit: 305607d32b32717cd3b2a3f53b112b6ca598e9a2

[felixbarny]

SGTM