perfglue: profiler stats need more than 1024 bytes

With a 1024 bytes buffer to display the stats, the end is truncated.
Use an array on the stack instead of leaking the buffer.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
mon,mds: call ceph_heap_profiler_init() at boot time

So that the CEPH_HEAP_PROFILER_INIT environment variable can be used to
start profiling.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
doc: update memory-profiling with examples

* Update the ceph tell from ceph daemon tell id to the new
  ceph tell deamon.id form

* Add usages examples for easier copy / paste

* Add MON to the list of daemons that can be profiled

* Document CEPH_HEAP_PROFILER_INIT=true

* Remove trailing empty lines

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #2629 from dachary/wip-heap-profiler

perfglue: minors heap profiler updates and documentation

Reviewed-by: Jianpeng Ma <majianpeng@gmail.com>