[10] RFR(XS): 8183534: [TEST] Make detection of compilation mode more robust

[Volker Simonis]

Hi,

can you please review the following trivial change which makes the
detection of compilation mode for JTreg more robust:

http://cr.openjdk.java.net/~simonis/webrevs/2017/8183534/
https://bugs.openjdk.java.net/browse/JDK-8183534

The compilation mode in JTreg is parsed from the "java.vm.info" system
property. The current implementation expects that "java.vm.info"
contains exactly one of the strings "mixed mode", "compiled mode" or
"interpreted mode" otherwise the detection will fail and JTreg will
quit with an error.

The detection can be done more robust by searching for the substrings
"mixed mode", "compiled mode" or "interpreted mode" instead, thus
allowing OpenJDK builders to store additional information in the
"java.vm.info" system property.

Thank you and best regards,
Volker