Error reporting should be improved for compiler CLI tests.

At the moment it looks like:

java.lang.RuntimeException: Expected to get exit value of [1]
    at com.oracle.java.testlibrary.OutputAnalyzer.shouldHaveExitValue(OutputAnalyzer.java:296)

TEST RESULT: Failed. Execution failed: `main' threw exception: java.lang.RuntimeException: Expected to get exit value of [1]

Such message does not tell much about what exactly went wrong.
Failed assertion above is from a test that verifies that an option is experimental, so its output should should contain short description of what happened, like:
'VM startup is expected to be failed without '-XX:-UnlockExperimentalVMOptions', because <option> is experimental, but VM statup succeeded with exit code 0'.