Openj9: IBM_JAVA_OPTIONS should only be checked if OPENJ9_JAVA_OPTIONS not set

[DanHeidinga]

The redirector only processes IBM_JAVA_OPTIONS if the OPENJ9 version isn't set:
https://github.com/eclipse/openj9/blob/9258a5aa4d1839d9df92d268dd4588a699576bdd/runtime/redirector/redirector.c#L534-L538

The vmargs.c code processes both options unconditionally:
https://github.com/eclipse/openj9/blob/a43aee9d618b9335d0a36f4b47eb0056ad8a8995/runtime/util/vmargs.c#L1394-L1395

The vmargs.c code should be updated to only read IBM_JAVA_OPTIONS if OPENJ9_JAVA_OPTIONS is not set.

Related to #3513

[DanHeidinga]

FYI @pdbain-ibm

[pdbain-ibm]

For the record, the redirector doesn't handle JAVA_TOOL_OPTIONS at all (and never has), while vmargs.c does (and always has). The redirector looks at the environment variable solely to choose the sidecar.

[pdbain-ibm]

FYI @pshipton and @gacholio
further to issue https://github.com/eclipse/openj9/issues/3478, particularly
https://github.com/eclipse/openj9/issues/3478#issuecomment-434695237 and
https://github.com/eclipse/openj9/issues/3478#issuecomment-435062184.

As I understand @DanHeidinga's intent, the arguments are the union of:

1. JAVA_TOOL_OPTIONS
2. OPENJ9_JAVA_OPTIONS
3. IBM_JAVA_OPTIONS (only if OPENJ9_JAVA_OPTIONS is not set)

Environment variables are processed in that order.

[pdbain-ibm]

Pull request https://github.com/eclipse/openj9/pull/3911 opened.