Don't set JAVA_HOME starting with ES 8.0

[dliappis]

Starting with Elasticsearch 8.0 (elastic/elasticsearch#69149) JAVA_HOME doesn't get honored. One should rely on ES_JAVA_HOME instead. This will also be supported starting with 7.12.0 having higher priority over JAVA_HOME and using JAVA_HOME will be deprecated.

Practically speaking for nightly benchmarks we generally rely on the bundled jdk, but if any user or internal tool needs to specify a different java version while we do add the bin directory in PATH we also specify JAVA_HOME which we define at least in

rally/esrally/mechanic/launcher.py

Line 176 in 5679af3

env["JAVA_HOME"] = java_home

.

As far as I understand we won't be broken right now given that JAVA_HOME/bin is in the PATH and Elasticsearch 8.0.0 will just ignore the environment variable JAVA_HOME. Therefore the priority for fixing this is not immediate.

Regarding the fix I think we need to:

1. Rely on ES_JAVA_HOME when the distribution-version is >=8.0.0
2. Rely on JAVA_HOME always when building Elasticsearch from source (when using the pipeline from-sources
3. Adjust and enhance unit tests/IT tests as required