Use separate arena for chunk tests.
Use separate arena for chunk tests.

This assures that side effects of internal allocation don't impact
tests.

jemalloc/jemalloc-cmake,wqfish/jemalloc,AndroidExternal/jemalloc,wqfish/jemalloc,leebaok/jemalloc-4.2.1-readcode,glandium/jemalloc,8l/jemalloc,wqfish/jemalloc,AndroidExternal/jemalloc,8l/jemalloc,leebaok/jemalloc-4.2.1-readcode,wqfish/jemalloc,jemalloc/jemalloc-cmake,8l/jemalloc,jemalloc/jemalloc-cmake,glandium/jemalloc,glandium/jemalloc,wqfish/jemalloc,leebaok/jemalloc-4.2.1-readcode,jemalloc/jemalloc-cmake,AndroidExternal/jemalloc,AndroidExternal/jemalloc,glandium/jemalloc,leebaok/jemalloc-4.2.1-readcode,8l/jemalloc