client.gnt_cluster: qualify IsBelowDir call
client.gnt_cluster: qualify IsBelowDir call

This fixes commit 4a89c117 ("Avoid backing up the export dir on cluster
upgrade").

Signed-off-by: Apollon Oikonomopoulos <ed81ed0a45ccd5c8869bda52e38353a6299ee39e@dmesg.gr>

ganeti/ganeti,ganeti/ganeti,mbakke/ganeti,mbakke/ganeti,ganeti/ganeti,mbakke/ganeti