ART: Disable part of reg_type_test for CMS

Disable the test for investigation. Figure out why FillHeap leaves
enough heap space available to allocate new array classes.

Test: ART_USE_READ_BARRIER=false m test-art-host-gtest-reg_type_test
Change-Id: I486651ae4bb2d96a7cc80583bc6557b88da3d9c1