RFR: JDK-8191923 Save run-test summary to file

[Magnus Ihse Bursie]

We should save the run-test summary to a file.

Bug: https://bugs.openjdk.java.net/browse/JDK-8191923
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8191923-save-run-test-summary-to-file/webrev.01

/Magnus