hotspot_custom is broken with jdk8

[sophia-guo]

hotspot_custom is broken with jdk8 due to change of JVM_NATIVE_OPTIONS in the playlist to -nativepath:"$(TESTIMAGE_PATH)/hotspot/jtreg/native" in #5370. This change meant to use TARGET=disabled.hotspot_custom to run openj9 custom serviceability jvmti test #5357 , which works by disabled.* target instead of hotspot_custom directly. I would prefer to separate a custom target to standardize the use of custom target. #5357 (comment) #5357 (comment)

https://ci.adoptium.net/view/Test_grinder/job/Grinder/10733/

11:08:52  TESTING:
11:08:52  Error: The -nativepath path does not exist: /hotspot/jtreg/native
11:08:52  Usage:

@LongyuZhang @llxia

[LongyuZhang]

Will separate the custom test for hotspot and j9 then.

[LongyuZhang]

Close this issue via #5493. Thanks.