client: fixed umount wrapper script (was complaining when only one parameter,...

client: fixed umount wrapper script (was complaining when only one parameter, e.g. the mount point, was used)

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1332 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534