RFR(M): 8178054: [TESTBUG] Need test for JVM TI IsModifiableModule

[serguei.spitsyn at oracle.com]

Please, review a JDK 9 fix for the test enhancement:
https://bugs.openjdk.java.net/browse/JDK-8178054

Webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2017/hotspot/8178054-jvmti-ismodif.2/


Summary:

   New JVMTI function IsModifiableModule() was introduced a couple of 
month ago.
   This patch adds a test coverage for it.

Testing:
   Tested the updated JTREG test serviceability/jvmti/GetNamedModule.


Thanks,
Serguei