RFR: 8273487: Zero: Handle "zero" variant in runtime tests [v2]

[Aleksey Shipilev]

> JDK-8179317 rewritten runtime shell tests to Java. There is a little omission in VM variant selection, which makes Zero fail some of the tier1 tests, like:
> 
> 
> $ CONF=linux-x86_64-zero-fastdebug make exploded-test TEST=runtime/StackGap/TestStackGap.java
> 
> STDERR:
> java.lang.Error: TESTBUG: unsupported vm variant
> at jdk.test.lib.Platform.variant(Platform.java:368)
> at jdk.test.lib.Platform.jvmLibDir(Platform.java:357)
> at jdk.test.lib.process.ProcessTools.addJvmLib(ProcessTools.java:585)
> at jdk.test.lib.process.ProcessTools.createNativeTestProcessBuilder(ProcessTools.java:575) 
> 
> 
> Additional testing:
>  - [x] Linux x86_64 Zero affected tests (StackGap, StackGuardPages, TestTLS) now run

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Build system awkwardness ensues

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5413/files
  - new: https://git.openjdk.java.net/jdk/pull/5413/files/141d8184..40998df5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5413&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5413&range=00-01

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5413.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5413/head:pull/5413

PR: https://git.openjdk.java.net/jdk/pull/5413