RFR(S) 8226645: [TESTBUG] some AppCDS tests relies on illegal reflective access

[Calvin Cheung]

bug: https://bugs.openjdk.java.net/browse/JDK-8226645

webrev: http://cr.openjdk.java.net/~ccheung/8226645/webrev.00/

Updating couple of AppCDS tests to use Lookup.defineClass instead of 
ClassLoader.defineClass. A dummy class will be loaded by the requested 
class loader and then a lookup instance is obtained using the 
privateLookupIn API.

Testing: mach5 tiers1 - 3.

              locally on linux-x64 with -vmoption:--illegal-access=deny

thanks,

Calvin