Fix os_cmd script for tty

Add the '-1' parameter to lxc-ls so each container is listed on a
single line, otherwise multiple container names were being listed
on a single line and causing the command to fail when in a tty.

Also use the '--filter' parameter to return only the utility
containers rather than having lxc-ls process and return each
container.

Change-Id: Ifcf1f13392d17464a088ce2928f434387ca39365

scripts/os-cmd

@@ -47,7 +47,7 @@ __check_cmd_avail ${LXCATTACH}
 __check_cmd_avail ${LXCLS}
 
 # Find the first utility container to execute in
-UTIL=$(${LXCLS} | grep utility | head -n 1)
+UTIL=$(${LXCLS} -1 --filter utility | head -n 1)
 if [ "z${UTIL}" == "z" ]; then
   echo "*** Couldn't find a utility container.  Exiting..."
   exit 1