storage: show gluster option in virsh --version=long

Adding output to 'virsh --version=long' makes it easier to
tell if a distro built with particular libraries (it doesn't
tell you what a remote libvirtd is built with, but is still
better than nothing).  But we forgot to mention gluster.

* tools/virsh.c (vshShowVersion): Add gluster witness.
Signed-off-by: NEric Blake <eblake@redhat.com>

tools/virsh.c

@@ -3068,6 +3068,9 @@ vshShowVersion(vshControl *ctl ATTRIBUTE_UNUSED)
 #endif
 #ifdef WITH_STORAGE_SHEEPDOG
     vshPrint(ctl, " Sheepdog");
+#endif
+#ifdef WITH_STORAGE_GLUSTER
+    vshPrint(ctl, " Gluster");
 #endif
     vshPrint(ctl, "\n");