RFR: JDK-8172912 JTReg concurrency value must be limited

[Magnus Ihse Bursie]

There is a limitation in jtreg that causes it to fail if called with 
-concurrency:X where X is > 50. This can happen on a multi-core machine, 
were we set the JOBS value to e.g. 64.

Bug: https://bugs.openjdk.java.net/browse/JDK-8172912

Patch inline:
diff --git a/test/Makefile b/test/Makefile
--- a/test/Makefile
+++ b/test/Makefile
@@ -60,7 +60,12 @@
  -include $(TOPDIR)/closed/test/Makefile

  ifeq ($(TEST_JOBS), 0)
-  JDK_TEST_JOBS=$(JOBS)
+  ifeq ($(shell $(EXPR) $(JOBS) \> 50), 1)
+    # JTReg cannot handle more than 50 in concurrency
+    JDK_TEST_JOBS=50
+  else
+    JDK_TEST_JOBS=$(JOBS)
+  endif
  else
    JDK_TEST_JOBS=$(TEST_JOBS)
  endif

/Magnus