Create helper methods for Jenkins computer api interactions

[M-Davies]

Part 1 of https://github.com/AdoptOpenJDK/openjdk-build/issues/2093

Introduce:

• https://ci.adoptopenjdk.net/job/build-scripts/job/jobs/job/<jdk_version>/job/<downstream_job_name>/<job_number>/consoleText Retrieve console log of a specific job (e.g. https://ci.adoptopenjdk.net/job/build-scripts/job/jobs/job/jdk/job/jdk-aix-ppc64-hotspot/241/consoleText)
• https://ci.adoptopenjdk.net/label/<nodelabel_combo>/api/json?pretty=true Returns information on a node label combination (e.g. https://ci.adoptopenjdk.net/label/win2012&&vs2017&&build&&windows&&x64/api/json?pretty=true)
• https://ci.adoptopenjdk.net/computer/<nodename>/api/json?pretty=true Returns information on a specific node name (e.g. https://ci.adoptopenjdk.net/computer/build-softlayer-win2012r2-x64-2/api/json?pretty=true)