8273487: Zero: Handle "zero" variant in runtime tests

Reviewed-by: alanb, dholmes

test/lib/jdk/test/lib/Platform.java

@@ -364,6 +364,11 @@ public class Platform {
             return "client";
         } else if (Platform.isMinimal()) {
             return "minimal";
+        } else if (Platform.isZero()) {
+            // This name is used to search for libjvm.so. Weirdly, current
+            // build system puts libjvm.so into default location, which is
+            // "server". See JDK-8273494.
+            return "server";
         } else {
             throw new Error("TESTBUG: unsupported vm variant");
         }