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/4527
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
mount.glusterfs: Introduce mem-accounting as an option

option mem-accounting enables memory accounting for the client
process.

re-factored to keep options with values and options without values
in different sections of mount.glusterfs.

Change-Id: I54ebc31a1eae6d7a5ce7b0255cd7df74d37d46c1
BUG: 834465
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/4528
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>