Clone reference repository is looking for $HOME

[AdamBrousseau]

Describe the bug
https://github.com/AdoptOpenJDK/openjdk-tests/blame/fb7463af44f406b233def68085a7bfc5f4bb7e83/buildenv/jenkins/testJobTemplate#L204
#1484
I believe when this executes the job actually looks for $HOME/openjdk_cache instead of, for example /home/jenkins/openjdk_cache
I see this error on a machine which has the cache setup

Cloning the remote Git repository
Cloning repository https://github.com/AdoptOpenJDK/openjdk-tests.git
 > git init /home/jenkins/workspace/Test_openjdk8_j9_sanity.functional_ppc64le_linux_Nightly/openjdk-tests # timeout=10
ERROR: Reference path does not exist: $HOME/openjdk_cache

At OpenJ9 we pull this value based on what plaform we are running on as it changes from linux to osx to windows. Hardcoding it to /home/jenkins/openjdk_cache would be a slight improvement but it wouldn't help osx for example.

To Reproduce
Steps to reproduce the behavior (or Grinder rerun link):
Run a test job on a machine which has ~/openjdk_cache vs a machine which does not.

Expected behavior
Should find the cache.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
Add any other context about the problem here.

[AdamBrousseau]

My browser decided to double save this.
Dup #1789