hydra-build: Add system info to the subject and extra headers.

Dependencies

• [2] FHAVPTZ6 Hydra/23: added some X-headers with meta info in email notifications, added more descriptive status
• [3] KA45EBF5 * Send email if a build fails.
• [4] FYO6NECE hydra
• [5] AJKTRRDJ rename var
• [6] OG7BEM57
• [*] 7YBYT2LQ

Change contents

• replacement in src/script/hydra-build at line 193
  [3.1209]→[2.702:781](∅→∅)
  − Subject => "Hydra job $jobName build " . $build->id . ": $status",
  [3.1209]

  [2.781]
  + Subject => "Hydra job $jobName on " . $build->system . ", build " . $build->id . ": $status",
• replacement in src/script/hydra-build at line 198
  [2.935]→[2.935:987](∅→∅)
  − 'X-Hydra-Job' => $build->job->name
  [2.935]

  [3.760]
  + 'X-Hydra-Job' => $build->job->name,

  + 'X-Hydra-System' => $build->system