RFR(S): 8159818: Convert IHOP_test to GTest

[Kirill Zhaldybin]

Dear all,

Could you please review this fix for 8159818?

Two tests were converted to GTest.
Since these tests require G1 GC, checks were added to prevent them to be 
run with other GCs.
Comments "// @requires UseG1GC" were added to facilitate finding such tests.

WebRev: http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8159818/webrev.00/
CR: https://bugs.openjdk.java.net/browse/JDK-8159818

Thank you.

Regards, Kirill