RFR 8226956: Add invocation tests for Graal and C1

[Harold Seigel]

Hi,

Please review this JDK-14 change to add invocation testing of Graal and 
C1.  The change also includes minor clean-ups of some invocation test code.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8226956/webrev/index.html

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8226956

The change was tested by running hs-tier3 tests on Linux-x64, Solaris, 
Windows, and Mac OS X.

Thanks, Harold