glusterd: Made gd_synctask_begin less 'monolithic' in terms of LOC.

Change-Id: I2dcaea56c2ca2c2c42c046ab7d2a39d586307868
BUG: 852147
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4507
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>