Add note on get_disks about unsupported guests

Put note out there in case others run into a failure using
SLES 11 images.

Change-Id: I34a87e533ffe903429913566a77ed5c6c05580cb
Closes-Bug: #1673607
diff --git a/tempest/common/utils/linux/remote_client.py b/tempest/common/utils/linux/remote_client.py
index 6dfc579..414c016 100644
--- a/tempest/common/utils/linux/remote_client.py
+++ b/tempest/common/utils/linux/remote_client.py
@@ -50,6 +50,8 @@
             ping_count=CONF.validation.ping_count,
             ping_size=CONF.validation.ping_size)
 
+    # Note that this method will not work on SLES11 guests, as they do
+    # not support the TYPE column on lsblk
     def get_disks(self):
         # Select root disk devices as shown by lsblk
         command = 'lsblk -lb --nodeps'