8160088: update hotspot tests depending on GC to use @requires vm.gc.X
Reviewed-by: iignatyev, mchernov, dholmes

8147075: Rename old GC JTreg tests to the new naming scheme
Summary: test/gc/7072527, test/gc/6845368, test/gc/6581734 renamed
Reviewed-by: jwilhelm, pliden