Better mechanism to handle memory accounting

Memory accounting will now be enabled if:

1) Any glusterfs process is spawned with argument --mem-accounting.
2) DEBUG is defined.

Change-Id: I3345e114127a57ce61916be0e2c4e0049a4c3432
BUG: 834465
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/4523
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>