RFR(S): 8170941: Executing gtest with invalid -Xlog argument crashes gtestLauncher

[Marcus Larsson]

Hi,

Please review the following small patch to prevent the gtest runner from 
crashing if invalid VM arguments are passed in.
The launcher will now exit with an error message rather than hit some 
assert in the half initialized VM.

Issue:
https://bugs.openjdk.java.net/browse/JDK-8170941

Webrev:
http://cr.openjdk.java.net/~mlarsson/8170941/webrev.00

Thanks,
Marcus