qa: use dump_metrics as alternative of get_heap_property

qa: use dump_metrics as alternative of get_heap_property

"get_heap_property *" asock commands are exposed to operators
to check the tcmalloc internals for understanding the performance
of the memory subsystem. but crimson uses the builtin seastar allocator
which is not backed by tcmalloc. but we can dump the metrics using
the "dump_metrics" asock command which is only available from
crimson-osd.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
Signed-off-by: Kefu Chai <kchai@redhat.com>