Raise default glusterfs version to 3.8

Change-Id: Ibafd332e616a1f3efacfccf67aaac8dd16ca8037
diff --git a/linux/system/repo/glusterfs.yml b/linux/system/repo/glusterfs.yml
index 3dfa9f9..fb331f0 100644
--- a/linux/system/repo/glusterfs.yml
+++ b/linux/system/repo/glusterfs.yml
@@ -1,9 +1,11 @@
 parameters:
+  _param:
+    glusterfs_version: 3.8
   linux:
     system:
       repo:
         glusterfs-ppa:
-          source: "deb http://ppa.launchpad.net/gluster/glusterfs-3.7/ubuntu ${_param:linux_system_codename} main"
+          source: "deb http://ppa.launchpad.net/gluster/glusterfs-${_param:glusterfs_version}/ubuntu ${_param:linux_system_codename} main"
           architectures: amd64
           key_id: 3FE869A9
-          key_server: keyserver.ubuntu.com
\ No newline at end of file
+          key_server: keyserver.ubuntu.com