RFR: JDK-8237914: The test-make target does not fail on test failure

[Erik Joelsson]

When running the make tests for the build itself, RunTest.gmk currently 
does not attempt at parsing the results. Because of this, failures 
aren't detected and so the build does not fail if a test fails. This 
patch adds a very rudimentary parsing, defining the whole test run as 1 
test and success/fail based on the exit code. With this, a test failure 
will cause the top level make to exit with error. I've verified that the 
testmake tests are still clean on all relevant platforms (as our CI 
would have failed to notice failures for a while).

Webrev: http://cr.openjdk.java.net/~erikj/8237914/webrev.01/

Bug: https://bugs.openjdk.java.net/browse/JDK-8237914

/Erik