Update references to the maillinglist to gluster-devel@gluster.org

gluster-devel@nongnu.org has moved to gluster-devel@gluster.org. All
occurrences in the current (non legacy) documentation and code have been
adjusted.

Change-Id: I053162e633f7ea14fd3eed239ded017df165147c
BUG: 1091705
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/7573
Reviewed-by: Justin Clift <justin@gluster.org>
Reviewed-by: Anand Avati <avati@redhat.com>
Tested-by: Anand Avati <avati@redhat.com>